diff --git a/CHANGELOG.md b/CHANGELOG.md
index 30de936..06b2d01 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Adding explicit support for Python `3.12`.
 - Publicly expose `requests_auth.SupportMultiAuth`, allowing multiple authentication support for every `requests` authentication class that exists.
 - Publicly expose `requests_auth.TokenMemoryCache`, allowing to create custom Oauth2 token cache based on this default implementation.
+- You can now provide your own HTML success (`success_html`) and failure (`failure_html`) display via the new `OAuth2.display` shared setting. Refer to documentation for more details.
 - Thanks to the new `redirect_uri_domain` parameter on Authorization code (with and without PKCE) and Implicit flows, you can now provide the [FQDN](https://en.wikipedia.org/wiki/Fully_qualified_domain_name) to use in the `redirect_uri` when `localhost` (the default) is not allowed.
 - `requests_auth.WakaTimeAuthorizationCode` handling access to the [WakaTime API](https://wakatime.com/developers).
 
@@ -19,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `requests_auth.JsonTokenFileCache` does not expose `tokens_path` or `last_save_time` attributes anymore and is also allowing `pathlib.Path` instances as cache location.
 - `requests_auth.TokenMemoryCache` does not expose `forbid_concurrent_cache_access` or `forbid_concurrent_missing_token_function_call` attributes anymore.
 - Browser display settings have been moved to a shared setting, see documentation for more information on `requests_auth.OAuth2.display`.
+  The failure page will be displayed for 10 seconds by default instead of 5 seconds previously.
   As a result the following classes no longer expose `success_display_time` and `failure_display_time` parameters.
   - `requests_auth.OAuth2AuthorizationCode`.
   - `requests_auth.OktaAuthorizationCode`.
@@ -30,6 +32,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - `requests_auth.AzureActiveDirectoryImplicitIdToken`.
   - `requests_auth.OktaImplicit`.
   - `requests_auth.OktaImplicitIdToken`.
+- The authentication success and failure displayed in the browser were revamped to be more user-friendly. `requests_auth.testing` was modified to accommodate this change:
+  - `tab.assert_success` `expected_message` parameter was removed.
+  - `tab.assert_failure` `expected_message` parameter should not be prefixed with `Unable to properly perform authentication: ` anymore and `\n` in the message should be replaced with `<br>`.
 
 ### Fixed
 - Type information is now provided following [PEP 561](https://www.python.org/dev/peps/pep-0561/).
diff --git a/README.md b/README.md
index a9b1881..af4e947 100644
--- a/README.md
+++ b/README.md
@@ -5,7 +5,7 @@
 <a href="https://github.com/Colin-b/requests_auth/actions"><img alt="Build status" src="https://github.com/Colin-b/requests_auth/workflows/Release/badge.svg"></a>
 <a href="https://github.com/Colin-b/requests_auth/actions"><img alt="Coverage" src="https://img.shields.io/badge/coverage-100%25-brightgreen"></a>
 <a href="https://github.com/psf/black"><img alt="Code style: black" src="https://img.shields.io/badge/code%20style-black-000000.svg"></a>
-<a href="https://github.com/Colin-b/requests_auth/actions"><img alt="Number of tests" src="https://img.shields.io/badge/tests-311 passed-blue"></a>
+<a href="https://github.com/Colin-b/requests_auth/actions"><img alt="Number of tests" src="https://img.shields.io/badge/tests-363 passed-blue"></a>
 <a href="https://pypi.org/project/requests-auth/"><img alt="Number of downloads" src="https://img.shields.io/pypi/dm/requests_auth"></a>
 </p>
 
@@ -703,7 +703,9 @@ The following parameters can be provided to `DisplaySettings`:
 | Name                   | Description                                                                                                                                                                      | Default value |
 |:-----------------------|:---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|:--------------|
 | `success_display_time` | In case a code or token is successfully received, this is the maximum amount of milliseconds the success page will be displayed in your browser.                                 | 1             |
-| `failure_display_time` | In case received code or token is not valid, this is the maximum amount of milliseconds the failure page will be displayed in your browser.                                      | 5_000         |
+| `success_html`         | In case a code or token is successfully received, this is the success page that will be displayed in your browser. `{display_time}` is expected in this content.                 |               |
+| `failure_display_time` | In case received code or token is not valid, this is the maximum amount of milliseconds the failure page will be displayed in your browser.                                      | 10_000        |
+| `failure_html`         | In case received code or token is not valid, this is the failure page that will be displayed in your browser. `{information}` and `{display_time}` are expected in this content. |               |
 
 ## API key in header
 
@@ -911,9 +913,7 @@ def test_something(browser_mock: BrowserMock):
 
     # perform code using authentication
 
-    tab.assert_success(
-        "You are now authenticated on 1234 You may close this tab."
-    )
+    tab.assert_success()
 ```
 
 ## Endorsements
diff --git a/requests_auth/_oauth2/authentication_responses_server.py b/requests_auth/_oauth2/authentication_responses_server.py
index 0240d21..1a49526 100644
--- a/requests_auth/_oauth2/authentication_responses_server.py
+++ b/requests_auth/_oauth2/authentication_responses_server.py
@@ -36,7 +36,10 @@ def do_GET(self):
             self.server.request_error = e
             logger.exception("Unable to properly perform authentication.")
             self.send_html(
-                self.error_page(f"Unable to properly perform authentication: {e}")
+                OAuth2.display.failure_html.format(
+                    display_time=OAuth2.display.failure_display_time,
+                    information=str(e).replace("\n", "<br>"),
+                )
             )
 
     def do_POST(self):
@@ -48,7 +51,10 @@ def do_POST(self):
             self.server.request_error = e
             logger.exception("Unable to properly perform authentication.")
             self.send_html(
-                self.error_page(f"Unable to properly perform authentication: {e}")
+                OAuth2.display.failure_html.format(
+                    display_time=OAuth2.display.failure_display_time,
+                    information=str(e).replace("\n", "<br>"),
+                )
             )
 
     def _parse_grant(self, arguments: dict):
@@ -67,15 +73,15 @@ def _parse_grant(self, arguments: dict):
         state = states[0]
         self.server.grant = state, grant
         self.send_html(
-            self.success_page(
-                f"You are now authenticated on {state}. You may close this tab."
+            OAuth2.display.success_html.format(
+                display_time=OAuth2.display.success_display_time
             )
         )
 
     def _get_form(self):
         content_length = int(self.headers.get("Content-Length", 0))
         body_str = self.rfile.read(content_length).decode("utf-8")
-        return parse_qs(body_str, keep_blank_values=1)
+        return parse_qs(body_str, keep_blank_values=True)
 
     def _get_params(self):
         return parse_qs(urlparse(self.path).query)
@@ -87,28 +93,6 @@ def send_html(self, html_content: str):
         self.wfile.write(str.encode(html_content))
         logger.debug("HTML content sent to client.")
 
-    def success_page(self, text: str):
-        return f"""<body onload="window.open('', '_self', ''); window.setTimeout(close, {OAuth2.display.success_display_time})" style="
-        color: #4F8A10;
-        background-color: #DFF2BF;
-        font-size: xx-large;
-        display: flex;
-        align-items: center;
-        justify-content: center;">
-            <div style="border: 1px solid;">{text}</div>
-        </body>"""
-
-    def error_page(self, text: str):
-        return f"""<body onload="window.open('', '_self', ''); window.setTimeout(close, {OAuth2.display.failure_display_time})" style="
-        color: #D8000C;
-        background-color: #FFBABA;
-        font-size: xx-large;
-        display: flex;
-        align-items: center;
-        justify-content: center;">
-            <div style="border: 1px solid;">{text}</div>
-        </body>"""
-
     def fragment_redirect_page(self):
         """Return a page with JS that calls back the server on the url
         original url: scheme://FQDN/path#fragment
@@ -180,7 +164,7 @@ def request_new_grant(grant_details: GrantDetails) -> (str, str):
     :raises InvalidGrantRequest: If the request was invalid.
     :raises TimeoutOccurred: If not retrieved within timeout.
     :raises GrantNotProvided: If grant is not provided in response (but no error occurred).
-    :raises StateNotProvided: If state if not provided in addition to the grant.
+    :raises StateNotProvided: If state is not provided in addition to the grant.
     """
     logger.debug(f"Requesting new {grant_details.name}...")
 
diff --git a/requests_auth/_oauth2/browser.py b/requests_auth/_oauth2/browser.py
index dba045c..2ee4c8d 100644
--- a/requests_auth/_oauth2/browser.py
+++ b/requests_auth/_oauth2/browser.py
@@ -31,22 +31,122 @@ def __init__(self, kwargs):
 
 
 class DisplaySettings:
+    _default_template = """<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <title>{title}</title>
+        <style>
+body {{
+    border: none;
+    box-sizing: border-box;
+    display: block;
+    font-family: "Segoe UI";
+    font-weight: 500;
+    line-height: 1.5;
+    padding: 50px 0 76px 0;
+    text-align: center;
+}}
+
+.content {{
+    padding: 30px 0 50px 0;
+}}
+
+h1 {{
+    color: {color};
+    font-size: 2.4rem;
+    margin: 1.7rem auto .5rem auto;
+}}
+
+p {{
+    color: #2f374f;
+    font-size: 1.2rem;
+    margin: .75rem 0 0 0;
+}}
+
+.btn {{
+    display: inline-block;
+    color: {color} !important;
+    text-decoration: none;
+    background-color: {background_color};
+    padding: 14px 24px;
+    border-radius: 8px;
+    font-size: 1em;
+    font-weight: 400;
+    margin: 50px 0 0 0;
+}}
+
+.btn:hover {{
+    color: {background_color} !important;
+    background-color: {color};
+}}
+
+@keyframes zoomText {{
+  from {{
+    opacity: 0;
+    transform: scale3d(0.9, 0.9, 0.9);
+  }}
+  50% {{
+    opacity: 1;
+  }}
+}}
+
+.content h1 {{
+    animation-duration: .6s;
+    animation-fill-mode: both;
+    animation-name: zoomText;
+    animation-delay: .2s;
+}}
+        </style>
+    </head>
+    <body onload="window.open('', '_self', ''); window.setTimeout(close, {display_time})">
+        <div class="content">
+            <h1>{title}</h1>
+            <p>{information}</p>
+        </div>
+        <div class="more">
+            <a href="https://colin-b.github.io/requests_auth/" class="btn" target="_blank" rel="noreferrer noopener" role="button">Documentation</a>
+            <a href="https://github.com/Colin-b/requests_auth/blob/develop/CHANGELOG.md" class="btn" target="_blank" rel="noreferrer noopener" role="button">Latest changes</a>
+        </div>
+    </body>
+</html>"""
+    _default_success = (
+        _default_template.replace("{title}", "Authentication success")
+        .replace("{color}", "#32cd32")
+        .replace("{background_color}", "#f0fff0")
+        .replace("{information}", "You can close this tab")
+    )
+    _default_failure = (
+        _default_template.replace("{title}", "Authentication failed")
+        .replace("{color}", "#dc143c")
+        .replace("{background_color}", "#fffafa")
+    )
+
     def __init__(
         self,
         *,
         success_display_time: int = 1,
-        failure_display_time: int = 5_000,
+        success_html: str = None,
+        failure_display_time: int = 10_000,
+        failure_html: str = None,
     ):
         """
         :param success_display_time: In case a code/token is successfully received,
         this is the maximum amount of milliseconds the success page will be displayed in your browser.
         Display the page for 1 millisecond by default.
+        :param success_html: In case a code or token is successfully received,
+        this is the success page that will be displayed in your browser.
+        `{display_time}` is expected in this content.
         :param failure_display_time: In case received code/token is not valid,
         this is the maximum amount of milliseconds the failure page will be displayed in your browser.
-        Display the page for 5 seconds by default.
+        Display the page for 10 seconds by default.
+        :param failure_html: In case received code or token is not valid,
+        this is the failure page that will be displayed in your browser.
+        `{information}` and `{display_time}` are expected in this content.
         """
         # Time is expressed in milliseconds
         self.success_display_time = success_display_time
+        self.success_html = success_html or self._default_success
 
         # Time is expressed in milliseconds
         self.failure_display_time = failure_display_time
+        self.failure_html = failure_html or self._default_failure
diff --git a/requests_auth/testing.py b/requests_auth/testing.py
index 1e8fe1e..ce70470 100644
--- a/requests_auth/testing.py
+++ b/requests_auth/testing.py
@@ -34,10 +34,177 @@ class Tab(threading.Thread):
       * assert the content sent to the browser
     """
 
-    def __init__(self, reply_url: str, data: str):
+    def __init__(
+        self,
+        reply_url: str,
+        data: str,
+        displayed_html: Optional[str] = None,
+    ):
         self.reply_url = reply_url
         self.data = data.encode() if data is not None else None
         self.checked = False
+        self.success_html = (
+            displayed_html
+            or """<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <title>Authentication success</title>
+        <style>
+body {{
+    border: none;
+    box-sizing: border-box;
+    display: block;
+    font-family: "Segoe UI";
+    font-weight: 500;
+    line-height: 1.5;
+    padding: 50px 0 76px 0;
+    text-align: center;
+}}
+
+.content {{
+    padding: 30px 0 50px 0;
+}}
+
+h1 {{
+    color: #32cd32;
+    font-size: 2.4rem;
+    margin: 1.7rem auto .5rem auto;
+}}
+
+p {{
+    color: #2f374f;
+    font-size: 1.2rem;
+    margin: .75rem 0 0 0;
+}}
+
+.btn {{
+    display: inline-block;
+    color: #32cd32 !important;
+    text-decoration: none;
+    background-color: #f0fff0;
+    padding: 14px 24px;
+    border-radius: 8px;
+    font-size: 1em;
+    font-weight: 400;
+    margin: 50px 0 0 0;
+}}
+
+.btn:hover {{
+    color: #f0fff0 !important;
+    background-color: #32cd32;
+}}
+
+@keyframes zoomText {{
+  from {{
+    opacity: 0;
+    transform: scale3d(0.9, 0.9, 0.9);
+  }}
+  50% {{
+    opacity: 1;
+  }}
+}}
+
+.content h1 {{
+    animation-duration: .6s;
+    animation-fill-mode: both;
+    animation-name: zoomText;
+    animation-delay: .2s;
+}}
+        </style>
+    </head>
+    <body onload="window.open('', '_self', ''); window.setTimeout(close, {display_time})">
+        <div class="content">
+            <h1>Authentication success</h1>
+            <p>You can close this tab</p>
+        </div>
+        <div class="more">
+            <a href="https://colin-b.github.io/requests_auth/" class="btn" target="_blank" rel="noreferrer noopener" role="button">Documentation</a>
+            <a href="https://github.com/Colin-b/requests_auth/blob/develop/CHANGELOG.md" class="btn" target="_blank" rel="noreferrer noopener" role="button">Latest changes</a>
+        </div>
+    </body>
+</html>"""
+        )
+        self.failure_html = (
+            displayed_html
+            or """<!DOCTYPE html>
+<html lang="en">
+    <head>
+        <title>Authentication failed</title>
+        <style>
+body {{
+    border: none;
+    box-sizing: border-box;
+    display: block;
+    font-family: "Segoe UI";
+    font-weight: 500;
+    line-height: 1.5;
+    padding: 50px 0 76px 0;
+    text-align: center;
+}}
+
+.content {{
+    padding: 30px 0 50px 0;
+}}
+
+h1 {{
+    color: #dc143c;
+    font-size: 2.4rem;
+    margin: 1.7rem auto .5rem auto;
+}}
+
+p {{
+    color: #2f374f;
+    font-size: 1.2rem;
+    margin: .75rem 0 0 0;
+}}
+
+.btn {{
+    display: inline-block;
+    color: #dc143c !important;
+    text-decoration: none;
+    background-color: #fffafa;
+    padding: 14px 24px;
+    border-radius: 8px;
+    font-size: 1em;
+    font-weight: 400;
+    margin: 50px 0 0 0;
+}}
+
+.btn:hover {{
+    color: #fffafa !important;
+    background-color: #dc143c;
+}}
+
+@keyframes zoomText {{
+  from {{
+    opacity: 0;
+    transform: scale3d(0.9, 0.9, 0.9);
+  }}
+  50% {{
+    opacity: 1;
+  }}
+}}
+
+.content h1 {{
+    animation-duration: .6s;
+    animation-fill-mode: both;
+    animation-name: zoomText;
+    animation-delay: .2s;
+}}
+        </style>
+    </head>
+    <body onload="window.open('', '_self', ''); window.setTimeout(close, {display_time})">
+        <div class="content">
+            <h1>Authentication failed</h1>
+            <p>{information}</p>
+        </div>
+        <div class="more">
+            <a href="https://colin-b.github.io/requests_auth/" class="btn" target="_blank" rel="noreferrer noopener" role="button">Documentation</a>
+            <a href="https://github.com/Colin-b/requests_auth/blob/develop/CHANGELOG.md" class="btn" target="_blank" rel="noreferrer noopener" role="button">Latest changes</a>
+        </div>
+    </body>
+</html>"""
+        )
         super().__init__()
 
     def run(self) -> None:
@@ -50,7 +217,7 @@ def run(self) -> None:
         # Simulate a browser tab token redirect to the reply URL
         self.content = self._simulate_redirect().decode()
 
-    def _request_favicon(self):
+    def _request_favicon(self) -> None:
         scheme, netloc, *_ = urlsplit(self.reply_url)
         favicon_response = urllib.request.urlopen(f"{scheme}://{netloc}/favicon.ico")
         assert favicon_response.read() == b"Favicon is not provided."
@@ -76,19 +243,15 @@ def _simulate_requests_auth_redirect(self) -> bytes:
         )
         return urllib.request.urlopen(reply_url, data=self.data).read()
 
-    def assert_success(self, expected_message: str, timeout: int = 1):
+    def assert_success(self, timeout: int = 1) -> None:
         self.join()
-        assert (
-            self.content
-            == f"<body onload=\"window.open('', '_self', ''); window.setTimeout(close, {timeout})\" style=\"\n        color: #4F8A10;\n        background-color: #DFF2BF;\n        font-size: xx-large;\n        display: flex;\n        align-items: center;\n        justify-content: center;\">\n            <div style=\"border: 1px solid;\">{expected_message}</div>\n        </body>"
-        )
+        assert self.content == self.success_html.format(display_time=timeout)
         self.checked = True
 
-    def assert_failure(self, expected_message: str, timeout: int = 5000):
+    def assert_failure(self, expected_message: str, timeout: int = 10_000) -> None:
         self.join()
-        assert (
-            self.content
-            == f"<body onload=\"window.open('', '_self', ''); window.setTimeout(close, {timeout})\" style=\"\n        color: #D8000C;\n        background-color: #FFBABA;\n        font-size: xx-large;\n        display: flex;\n        align-items: center;\n        justify-content: center;\">\n            <div style=\"border: 1px solid;\">{expected_message}</div>\n        </body>"
+        assert self.content == self.failure_html.format(
+            display_time=timeout, information=expected_message
         )
         self.checked = True
 
@@ -97,7 +260,7 @@ class BrowserMock:
     def __init__(self):
         self.tabs: Dict[str, Tab] = {}
 
-    def open(self, url: str, new: int):
+    def open(self, url: str, new: int) -> bool:
         assert new == 1
         assert url in self.tabs, f"Browser call on {url} was not mocked."
         # Simulate a browser by sending the response in another thread
@@ -105,18 +268,23 @@ def open(self, url: str, new: int):
         return True
 
     def add_response(
-        self, opened_url: str, reply_url: Optional[str], data: str = None
+        self,
+        opened_url: str,
+        reply_url: Optional[str],
+        data: Optional[str] = None,
+        displayed_html: Optional[str] = None,
     ) -> Tab:
         """
         :param opened_url: URL opened by requests_auth
         :param reply_url: The URL to send a response to, None to simulate the fact that there is no redirect.
         :param data: Body of the POST response to be sent. None to send a GET request.
+        :param displayed_html: Expected success/failure page.
         """
-        tab = Tab(reply_url, data)
+        tab = Tab(reply_url, data, displayed_html)
         self.tabs[opened_url] = tab
         return tab
 
-    def assert_checked(self):
+    def assert_checked(self) -> None:
         for url, tab in self.tabs.items():
             tab.join()
             assert tab.checked, f"Response received on {url} was not checked properly."
diff --git a/tests/features/multi_auth/test_add_operator.py b/tests/features/multi_auth/test_add_operator.py
index 9605b8f..8a4f6bc 100644
--- a/tests/features/multi_auth/test_add_operator.py
+++ b/tests/features/multi_auth/test_add_operator.py
@@ -360,9 +360,7 @@ def test_oauth2_authorization_code_and_api_key_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_and_multiple_authentication_can_be_combined(
@@ -406,9 +404,7 @@ def test_oauth2_authorization_code_and_multiple_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_and_api_key_authentication_can_be_combined(
@@ -451,9 +447,7 @@ def test_oauth2_pkce_and_api_key_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_and_multiple_authentication_can_be_combined(
@@ -500,9 +494,7 @@ def test_oauth2_pkce_and_multiple_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_and_api_key_authentication_can_be_combined(
@@ -535,9 +527,7 @@ def test_oauth2_implicit_and_api_key_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_and_multiple_authentication_can_be_combined(
@@ -574,6 +564,4 @@ def test_oauth2_implicit_and_multiple_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
diff --git a/tests/features/multi_auth/test_and_operator.py b/tests/features/multi_auth/test_and_operator.py
index b08a78d..4abe2af 100644
--- a/tests/features/multi_auth/test_and_operator.py
+++ b/tests/features/multi_auth/test_and_operator.py
@@ -360,9 +360,7 @@ def test_oauth2_authorization_code_and_api_key_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_and_multiple_authentication_can_be_combined(
@@ -406,9 +404,7 @@ def test_oauth2_authorization_code_and_multiple_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_and_api_key_authentication_can_be_combined(
@@ -451,9 +447,7 @@ def test_oauth2_pkce_and_api_key_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_and_multiple_authentication_can_be_combined(
@@ -500,9 +494,7 @@ def test_oauth2_pkce_and_multiple_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_and_api_key_authentication_can_be_combined(
@@ -535,9 +527,7 @@ def test_oauth2_implicit_and_api_key_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_and_multiple_authentication_can_be_combined(
@@ -574,6 +564,4 @@ def test_oauth2_implicit_and_multiple_authentication_can_be_combined(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
diff --git a/tests/oauth2/authorization_code/test_oauth2_authorization_code.py b/tests/oauth2/authorization_code/test_oauth2_authorization_code.py
index f54e962..60012d6 100644
--- a/tests/oauth2/authorization_code/test_oauth2_authorization_code.py
+++ b/tests/oauth2/authorization_code/test_oauth2_authorization_code.py
@@ -47,9 +47,7 @@ def test_oauth2_authorization_code_flow_uses_provided_session(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_uses_redirect_uri_domain(
@@ -91,8 +89,73 @@ def test_oauth2_authorization_code_flow_uses_redirect_uri_domain(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
+    tab.assert_success()
+
+
+def test_oauth2_authorization_code_flow_uses_custom_success(
+    token_cache, responses: RequestsMock, browser_mock: BrowserMock
+):
+    auth = requests_auth.OAuth2AuthorizationCode(
+        "http://provide_code",
+        "http://provide_access_token",
+    )
+    requests_auth.OAuth2.display.success_html = (
+        "<body><div>SUCCESS: {display_time}</div></body>"
+    )
+    tab = browser_mock.add_response(
+        opened_url="http://provide_code?response_type=code&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de",
+        displayed_html="<body><div>SUCCESS: {display_time}</div></body>",
+    )
+    responses.post(
+        "http://provide_access_token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match=[
+            urlencoded_params_matcher(
+                {
+                    "grant_type": "authorization_code",
+                    "redirect_uri": "http://localhost:5000/",
+                    "response_type": "code",
+                    "code": "SplxlOBeZQQYbYS6WxSbIA",
+                }
+            ),
+        ],
+    )
+    responses.get(
+        "http://authorized_only",
+        match=[header_matcher({"Authorization": "Bearer 2YotnFZFEjr1zCsicMWpAA"})],
+    )
+
+    requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_success()
+
+
+def test_oauth2_authorization_code_flow_uses_custom_failure(
+    token_cache, browser_mock: BrowserMock
+):
+    auth = requests_auth.OAuth2AuthorizationCode(
+        "http://provide_code",
+        "http://provide_access_token",
+    )
+    requests_auth.OAuth2.display.failure_html = "FAILURE: {display_time}\n{information}"
+    tab = browser_mock.add_response(
+        opened_url="http://provide_code?response_type=code&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#error=invalid_request",
+        displayed_html="FAILURE: {display_time}\n{information}",
+    )
+
+    with pytest.raises(requests_auth.InvalidGrantRequest):
+        requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_failure(
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -133,9 +196,7 @@ def test_oauth2_authorization_code_flow_get_code_is_sent_in_authorization_header
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_token_is_expired_after_30_seconds_by_default(
@@ -182,9 +243,7 @@ def test_oauth2_authorization_code_flow_token_is_expired_after_30_seconds_by_def
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_client_credentials_flow_token_custom_expiry(
@@ -244,9 +303,7 @@ def test_refresh_token(token_cache, responses: RequestsMock, browser_mock: Brows
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
     # response for refresh token grant
     responses.post(
@@ -313,9 +370,7 @@ def test_refresh_token_invalid(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
     # response for refresh token grant
     responses.post(
         "http://provide_access_token",
@@ -346,9 +401,7 @@ def test_refresh_token_invalid(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_refresh_token_access_token_not_expired(
@@ -388,9 +441,7 @@ def test_refresh_token_access_token_not_expired(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
     # expect Bearer token to remain the same
     responses.get(
@@ -427,9 +478,7 @@ def test_empty_token_is_invalid(
         str(exception_info.value)
         == "access_token not provided within {'access_token': '', 'token_type': 'example', 'expires_in': 3600, 'refresh_token': 'tGzv3JOkF0XG5Qx2TlKWIA', 'example_parameter': 'example_value'}."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_no_json(
@@ -446,9 +495,7 @@ def test_with_invalid_grant_request_no_json(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "failure"
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error(
@@ -475,9 +522,7 @@ def test_with_invalid_grant_request_invalid_request_error(
         "includes multiple credentials, utilizes more than one mechanism for "
         "authenticating the client, or is otherwise malformed."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description(
@@ -498,9 +543,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc of the error"
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri(
@@ -528,9 +571,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on http://test_url"
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri_and_other_fields(
@@ -559,9 +600,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == "invalid_request: desc of the error\nMore information can be found on http://test_url\nAdditional information: {'other': 'other info'}"
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_without_error(
@@ -582,9 +621,7 @@ def test_with_invalid_grant_request_without_error(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "{'other': 'other info'}"
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_client_error(
@@ -615,9 +652,7 @@ def test_with_invalid_grant_request_invalid_client_error(
         'code and include the "WWW-Authenticate" response header field matching the '
         "authentication scheme used by the client."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_grant_error(
@@ -644,9 +679,7 @@ def test_with_invalid_grant_request_invalid_grant_error(
         "does not match the redirection URI used in the authorization request, or was "
         "issued to another client."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unauthorized_client_error(
@@ -671,9 +704,7 @@ def test_with_invalid_grant_request_unauthorized_client_error(
         == "unauthorized_client: The authenticated client is not authorized to use this "
         "authorization grant type."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unsupported_grant_type_error(
@@ -698,9 +729,7 @@ def test_with_invalid_grant_request_unsupported_grant_type_error(
         == "unsupported_grant_type: The authorization grant type is not supported by the "
         "authorization server."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_scope_error(
@@ -725,9 +754,7 @@ def test_with_invalid_grant_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, malformed, or "
         "exceeds the scope granted by the resource owner."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_token_request_invalid_request_error(
@@ -747,7 +774,7 @@ def test_with_invalid_token_request_invalid_request_error(
         == "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -764,9 +791,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc"
-    tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc"
-    )
+    tab.assert_failure("invalid_request: desc")
 
 
 def test_with_invalid_token_request_invalid_request_error_and_error_description_and_uri(
@@ -786,7 +811,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url"
+        "invalid_request: desc<br>More information can be found on http://test_url"
     )
 
 
@@ -807,7 +832,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
+        "invalid_request: desc<br>More information can be found on http://test_url<br>Additional information: {'other': ['test']}"
     )
 
 
@@ -828,7 +853,7 @@ def test_with_invalid_token_request_unauthorized_client_error(
         == "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
+        "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
 
 
@@ -849,7 +874,7 @@ def test_with_invalid_token_request_access_denied_error(
         == "access_denied: The resource owner or authorization server denied the request."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: access_denied: The resource owner or authorization server denied the request."
+        "access_denied: The resource owner or authorization server denied the request."
     )
 
 
@@ -870,7 +895,7 @@ def test_with_invalid_token_request_unsupported_response_type_error(
         == "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
+        "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
 
 
@@ -891,7 +916,7 @@ def test_with_invalid_token_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_scope: The requested scope is invalid, unknown, or malformed."
+        "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
 
 
@@ -912,7 +937,7 @@ def test_with_invalid_token_request_server_error_error(
         == "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -933,7 +958,7 @@ def test_with_invalid_token_request_temporarily_unavailable_error(
         == "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -974,9 +999,7 @@ def test_nonce_is_sent_if_provided_in_authorization_url(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_response_type_can_be_provided_in_url(
@@ -1017,9 +1040,7 @@ def test_response_type_can_be_provided_in_url(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 49b67a19e70f692c3fc09dd124e5782b41a86f4f4931e1cc938ccbb466eecf1b730edb9eb01e42005de77ce3dd5a016418f8e780f30c4477d71102fe03e39e62. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_authorization_url_is_mandatory():
diff --git a/tests/oauth2/authorization_code/test_oauth2_authorization_code_okta.py b/tests/oauth2/authorization_code/test_oauth2_authorization_code_okta.py
index 073b289..2b24009 100644
--- a/tests/oauth2/authorization_code/test_oauth2_authorization_code_okta.py
+++ b/tests/oauth2/authorization_code/test_oauth2_authorization_code_okta.py
@@ -51,9 +51,7 @@ def test_oauth2_authorization_code_flow_uses_provided_session(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_uses_redirect_uri_domain(
@@ -97,8 +95,75 @@ def test_oauth2_authorization_code_flow_uses_redirect_uri_domain(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
+    tab.assert_success()
+
+
+def test_oauth2_authorization_code_flow_uses_custom_success(
+    token_cache, responses: RequestsMock, browser_mock: BrowserMock
+):
+    auth = requests_auth.OktaAuthorizationCode(
+        "testserver.okta-emea.com",
+        "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+    )
+    requests_auth.OAuth2.display.success_html = (
+        "<body><div>SUCCESS: {display_time}</div></body>"
+    )
+    tab = browser_mock.add_response(
+        opened_url="https://testserver.okta-emea.com/oauth2/default/v1/authorize?client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b",
+        displayed_html="<body><div>SUCCESS: {display_time}</div></body>",
+    )
+    responses.post(
+        "https://testserver.okta-emea.com/oauth2/default/v1/token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match=[
+            urlencoded_params_matcher(
+                {
+                    "grant_type": "authorization_code",
+                    "redirect_uri": "http://localhost:5000/",
+                    "client_id": "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+                    "scope": "openid",
+                    "response_type": "code",
+                    "code": "SplxlOBeZQQYbYS6WxSbIA",
+                }
+            ),
+        ],
+    )
+    responses.get(
+        "http://authorized_only",
+        match=[header_matcher({"Authorization": "Bearer 2YotnFZFEjr1zCsicMWpAA"})],
+    )
+
+    requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_success()
+
+
+def test_oauth2_authorization_code_flow_uses_custom_failure(
+    token_cache, browser_mock: BrowserMock
+):
+    auth = requests_auth.OktaAuthorizationCode(
+        "testserver.okta-emea.com",
+        "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+    )
+    requests_auth.OAuth2.display.failure_html = "FAILURE: {display_time}\n{information}"
+    tab = browser_mock.add_response(
+        opened_url="https://testserver.okta-emea.com/oauth2/default/v1/authorize?client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#error=invalid_request",
+        displayed_html="FAILURE: {display_time}\n{information}",
+    )
+
+    with pytest.raises(requests_auth.InvalidGrantRequest):
+        requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_failure(
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -141,9 +206,7 @@ def test_okta_authorization_code_flow_get_code_is_sent_in_authorization_header_b
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_okta_authorization_code_flow_token_is_expired_after_30_seconds_by_default(
@@ -192,9 +255,7 @@ def test_okta_authorization_code_flow_token_is_expired_after_30_seconds_by_defau
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_okta_authorization_code_flow_token_custom_expiry(
@@ -245,9 +306,7 @@ def test_empty_token_is_invalid(
         str(exception_info.value)
         == "access_token not provided within {'access_token': '', 'token_type': 'example', 'expires_in': 3600, 'refresh_token': 'tGzv3JOkF0XG5Qx2TlKWIA', 'example_parameter': 'example_value'}."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_no_json(
@@ -268,9 +327,7 @@ def test_with_invalid_grant_request_no_json(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "failure"
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error(
@@ -297,9 +354,7 @@ def test_with_invalid_grant_request_invalid_request_error(
         "includes multiple credentials, utilizes more than one mechanism for "
         "authenticating the client, or is otherwise malformed."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description(
@@ -320,9 +375,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc of the error"
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri(
@@ -350,9 +403,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on http://test_url"
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri_and_other_fields(
@@ -381,9 +432,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == "invalid_request: desc of the error\nMore information can be found on http://test_url\nAdditional information: {'other': 'other info'}"
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_without_error(
@@ -404,9 +453,7 @@ def test_with_invalid_grant_request_without_error(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "{'other': 'other info'}"
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_client_error(
@@ -437,9 +484,7 @@ def test_with_invalid_grant_request_invalid_client_error(
         'code and include the "WWW-Authenticate" response header field matching the '
         "authentication scheme used by the client."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_grant_error(
@@ -466,9 +511,7 @@ def test_with_invalid_grant_request_invalid_grant_error(
         "does not match the redirection URI used in the authorization request, or was "
         "issued to another client."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unauthorized_client_error(
@@ -493,9 +536,7 @@ def test_with_invalid_grant_request_unauthorized_client_error(
         == "unauthorized_client: The authenticated client is not authorized to use this "
         "authorization grant type."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unsupported_grant_type_error(
@@ -520,9 +561,7 @@ def test_with_invalid_grant_request_unsupported_grant_type_error(
         == "unsupported_grant_type: The authorization grant type is not supported by the "
         "authorization server."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_scope_error(
@@ -547,9 +586,7 @@ def test_with_invalid_grant_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, malformed, or "
         "exceeds the scope granted by the resource owner."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_token_request_invalid_request_error(
@@ -569,7 +606,7 @@ def test_with_invalid_token_request_invalid_request_error(
         == "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -586,9 +623,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc"
-    tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc"
-    )
+    tab.assert_failure("invalid_request: desc")
 
 
 def test_with_invalid_token_request_invalid_request_error_and_error_description_and_uri(
@@ -608,7 +643,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url"
+        "invalid_request: desc<br>More information can be found on http://test_url"
     )
 
 
@@ -629,7 +664,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
+        "invalid_request: desc<br>More information can be found on http://test_url<br>Additional information: {'other': ['test']}"
     )
 
 
@@ -650,7 +685,7 @@ def test_with_invalid_token_request_unauthorized_client_error(
         == "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
+        "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
 
 
@@ -671,7 +706,7 @@ def test_with_invalid_token_request_access_denied_error(
         == "access_denied: The resource owner or authorization server denied the request."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: access_denied: The resource owner or authorization server denied the request."
+        "access_denied: The resource owner or authorization server denied the request."
     )
 
 
@@ -692,7 +727,7 @@ def test_with_invalid_token_request_unsupported_response_type_error(
         == "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
+        "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
 
 
@@ -713,7 +748,7 @@ def test_with_invalid_token_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_scope: The requested scope is invalid, unknown, or malformed."
+        "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
 
 
@@ -734,7 +769,7 @@ def test_with_invalid_token_request_server_error_error(
         == "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -755,7 +790,7 @@ def test_with_invalid_token_request_temporarily_unavailable_error(
         == "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
diff --git a/tests/oauth2/authorization_code/test_oauth2_authorization_code_wakatime.py b/tests/oauth2/authorization_code/test_oauth2_authorization_code_wakatime.py
index c134764..4f78cbe 100644
--- a/tests/oauth2/authorization_code/test_oauth2_authorization_code_wakatime.py
+++ b/tests/oauth2/authorization_code/test_oauth2_authorization_code_wakatime.py
@@ -49,9 +49,7 @@ def test_oauth2_authorization_code_flow_uses_provided_client(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_uses_redirect_uri_domain(
@@ -92,8 +90,73 @@ def test_oauth2_authorization_code_flow_uses_redirect_uri_domain(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
+    tab.assert_success()
+
+
+def test_oauth2_authorization_code_flow_uses_custom_success(
+    token_cache, responses: RequestsMock, browser_mock: BrowserMock
+):
+    auth = requests_auth.WakaTimeAuthorizationCode(
+        "jPJQV0op6Pu3b66MWDi8b1wD",
+        "waka_sec_0c4MBGeR9LN74LzV5uelF9SgeQ32CqfeWpIuieneBbsL57dAAlqqJWDiVDJOlsSx61pVwHMKlsb3uMvU",
+        scope="email",
+    )
+    requests_auth.OAuth2.display.success_html = (
+        "<body><div>SUCCESS: {display_time}</div></body>"
+    )
+    tab = browser_mock.add_response(
+        opened_url="https://wakatime.com/oauth/authorize?client_id=jPJQV0op6Pu3b66MWDi8b1wD&client_secret=waka_sec_0c4MBGeR9LN74LzV5uelF9SgeQ32CqfeWpIuieneBbsL57dAAlqqJWDiVDJOlsSx61pVwHMKlsb3uMvU&scope=email&response_type=code&state=5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a",
+        displayed_html="<body><div>SUCCESS: {display_time}</div></body>",
+    )
+    responses.post(
+        "https://wakatime.com/oauth/token",
+        body="access_token=waka_tok_12345&token_type=bearer&expires_in=3600&refresh_token=waka_ref_12345&scope=email&example_parameter=example_value",
+        content_type="text/html; charset=utf-8",
+        match=[
+            urlencoded_params_matcher(
+                {
+                    "grant_type": "authorization_code",
+                    "redirect_uri": "http://localhost:5000/",
+                    "client_id": "jPJQV0op6Pu3b66MWDi8b1wD",
+                    "client_secret": "waka_sec_0c4MBGeR9LN74LzV5uelF9SgeQ32CqfeWpIuieneBbsL57dAAlqqJWDiVDJOlsSx61pVwHMKlsb3uMvU",
+                    "scope": "email",
+                    "response_type": "code",
+                    "code": "SplxlOBeZQQYbYS6WxSbIA",
+                }
+            )
+        ],
+    )
+    responses.get(
+        "https://authorized_only",
+        match=[header_matcher({"Authorization": "Bearer waka_tok_12345"})],
+    )
+
+    requests.get("https://authorized_only", auth=auth)
+
+    tab.assert_success()
+
+
+def test_oauth2_authorization_code_flow_uses_custom_failure(
+    token_cache, browser_mock: BrowserMock
+):
+    auth = requests_auth.WakaTimeAuthorizationCode(
+        "jPJQV0op6Pu3b66MWDi8b1wD",
+        "waka_sec_0c4MBGeR9LN74LzV5uelF9SgeQ32CqfeWpIuieneBbsL57dAAlqqJWDiVDJOlsSx61pVwHMKlsb3uMvU",
+        scope="email",
+    )
+    requests_auth.OAuth2.display.failure_html = "FAILURE: {display_time}\n{information}"
+    tab = browser_mock.add_response(
+        opened_url="https://wakatime.com/oauth/authorize?client_id=jPJQV0op6Pu3b66MWDi8b1wD&client_secret=waka_sec_0c4MBGeR9LN74LzV5uelF9SgeQ32CqfeWpIuieneBbsL57dAAlqqJWDiVDJOlsSx61pVwHMKlsb3uMvU&scope=email&response_type=code&state=5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#error=invalid_request",
+        displayed_html="FAILURE: {display_time}\n{information}",
+    )
+
+    with pytest.raises(requests_auth.InvalidGrantRequest):
+        requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_failure(
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -134,9 +197,7 @@ def test_multiple_scopes_are_comma_separated(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 34f21f9ea8be7b1dfd3dd1673a9aea7c3a1737228b4f08bc11ebacb88449afaa658811f8022e9962927a0ec42805c0e3cc5e6b0d9185308216b298a686001a1f. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_get_code_is_sent_in_authorization_header_by_default(
@@ -176,9 +237,7 @@ def test_oauth2_authorization_code_flow_get_code_is_sent_in_authorization_header
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_json_response_is_handled_even_if_unused(
@@ -224,9 +283,7 @@ def test_json_response_is_handled_even_if_unused(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_get_code_is_expired_after_30_seconds_by_default(
@@ -273,9 +330,7 @@ def test_oauth2_authorization_code_flow_get_code_is_expired_after_30_seconds_by_
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_get_code_custom_expiry(
@@ -338,9 +393,7 @@ def test_oauth2_authorization_code_flow_refresh_token(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
     # response for refresh token grant
     responses.post(
@@ -405,9 +458,7 @@ def test_oauth2_authorization_code_flow_refresh_token_invalid(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
     # response for refresh token grant
     responses.post(
@@ -442,9 +493,7 @@ def test_oauth2_authorization_code_flow_refresh_token_invalid(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_authorization_code_flow_refresh_token_access_token_not_expired(
@@ -484,9 +533,7 @@ def test_oauth2_authorization_code_flow_refresh_token_access_token_not_expired(
 
     requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
     # expect Bearer token to remain the same
     requests.get("https://authorized_only", auth=auth)
@@ -530,9 +577,7 @@ def test_empty_token_is_invalid(
         str(exception_info.value)
         == "access_token not provided within {'access_token': '', 'token_type': 'bearer', 'expires_in': '3600', 'refresh_token': 'waka_ref_12345', 'scope': 'email', 'example_parameter': 'example_value'}."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_no_json(
@@ -557,9 +602,7 @@ def test_with_invalid_grant_request_no_json(
     with pytest.raises(requests_auth.InvalidGrantRequest, match="failure"):
         requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error(
@@ -590,9 +633,7 @@ def test_with_invalid_grant_request_invalid_request_error(
         "includes multiple credentials, utilizes more than one mechanism for "
         "authenticating the client, or is otherwise malformed."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description(
@@ -617,9 +658,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description(
         requests.get("https://authorized_only", auth=auth)
 
     assert str(exception_info.value) == "invalid_request: desc of the error"
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri(
@@ -651,9 +690,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on https://test_url"
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri_and_other_fields(
@@ -686,9 +723,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == "invalid_request: desc of the error\nMore information can be found on https://test_url\nAdditional information: {'other': 'other info'}"
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_without_error(
@@ -714,9 +749,7 @@ def test_with_invalid_grant_request_without_error(
     ):
         requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_client_error(
@@ -751,9 +784,7 @@ def test_with_invalid_grant_request_invalid_client_error(
         'code and include the "WWW-Authenticate" response header field matching the '
         "authentication scheme used by the client."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_grant_error(
@@ -784,9 +815,7 @@ def test_with_invalid_grant_request_invalid_grant_error(
         "does not match the redirection URI used in the authorization request, or was "
         "issued to another client."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unauthorized_client_error(
@@ -815,9 +844,7 @@ def test_with_invalid_grant_request_unauthorized_client_error(
         == "unauthorized_client: The authenticated client is not authorized to use this "
         "authorization grant type."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unsupported_grant_type_error(
@@ -846,9 +873,7 @@ def test_with_invalid_grant_request_unsupported_grant_type_error(
         == "unsupported_grant_type: The authorization grant type is not supported by the "
         "authorization server."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_scope_error(
@@ -877,9 +902,7 @@ def test_with_invalid_grant_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, malformed, or "
         "exceeds the scope granted by the resource owner."
     )
-    tab.assert_success(
-        "You are now authenticated on 5d0adb208bdbecaf5cfb6de0bf4ba0aea52986f3fc5ea7bc30c4b2db449c17e5c9d15f9a3926476cdaf1c72e9f73c7cfdc624dde0187c38d8c6b04532770df2a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_token_request_invalid_request_error(
@@ -903,7 +926,7 @@ def test_with_invalid_token_request_invalid_request_error(
         == "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -925,9 +948,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description(
     ):
         requests.get("https://authorized_only", auth=auth)
 
-    tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc"
-    )
+    tab.assert_failure("invalid_request: desc")
 
 
 def test_with_invalid_token_request_invalid_request_error_and_error_description_and_uri(
@@ -951,7 +972,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on https://test_url"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on https://test_url"
+        "invalid_request: desc<br>More information can be found on https://test_url"
     )
 
 
@@ -976,7 +997,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on https://test_url\nAdditional information: {'other': ['test']}"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on https://test_url\nAdditional information: {'other': ['test']}"
+        "invalid_request: desc<br>More information can be found on https://test_url<br>Additional information: {'other': ['test']}"
     )
 
 
@@ -1001,7 +1022,7 @@ def test_with_invalid_token_request_unauthorized_client_error(
         == "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
+        "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
 
 
@@ -1026,7 +1047,7 @@ def test_with_invalid_token_request_access_denied_error(
         == "access_denied: The resource owner or authorization server denied the request."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: access_denied: The resource owner or authorization server denied the request."
+        "access_denied: The resource owner or authorization server denied the request."
     )
 
 
@@ -1051,7 +1072,7 @@ def test_with_invalid_token_request_unsupported_response_type_error(
         == "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
+        "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
 
 
@@ -1076,7 +1097,7 @@ def test_with_invalid_token_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_scope: The requested scope is invalid, unknown, or malformed."
+        "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
 
 
@@ -1101,7 +1122,7 @@ def test_with_invalid_token_request_server_error_error(
         == "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -1126,7 +1147,7 @@ def test_with_invalid_token_request_temporarily_unavailable_error(
         == "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
diff --git a/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce.py b/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce.py
index cf5a23b..7bfb9f2 100644
--- a/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce.py
+++ b/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce.py
@@ -52,9 +52,7 @@ def test_oauth2_pkce_flow_uses_provided_session(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_flow_uses_redirect_uri_domain(
@@ -100,8 +98,80 @@ def test_oauth2_pkce_flow_uses_redirect_uri_domain(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
+    tab.assert_success()
+
+
+def test_oauth2_pkce_flow_uses_custom_success(
+    token_cache, responses: RequestsMock, monkeypatch, browser_mock: BrowserMock
+):
+    monkeypatch.setattr(
+        requests_auth._oauth2.authorization_code_pkce.os, "urandom", lambda x: b"1" * 63
+    )
+    auth = requests_auth.OAuth2AuthorizationCodePKCE(
+        "http://provide_code",
+        "http://provide_access_token",
+    )
+    requests_auth.OAuth2.display.success_html = (
+        "<body><div>SUCCESS: {display_time}</div></body>"
+    )
+    tab = browser_mock.add_response(
+        opened_url="http://provide_code?response_type=code&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&code_challenge=5C_ph_KZ3DstYUc965SiqmKAA-ShvKF4Ut7daKd3fjc&code_challenge_method=S256",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de",
+        displayed_html="<body><div>SUCCESS: {display_time}</div></body>",
+    )
+    responses.post(
+        "http://provide_access_token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match=[
+            urlencoded_params_matcher(
+                {
+                    "code_verifier": "MTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTEx",
+                    "grant_type": "authorization_code",
+                    "redirect_uri": "http://localhost:5000/",
+                    "response_type": "code",
+                    "code": "SplxlOBeZQQYbYS6WxSbIA",
+                }
+            ),
+        ],
+    )
+    responses.get(
+        "http://authorized_only",
+        match=[header_matcher({"Authorization": "Bearer 2YotnFZFEjr1zCsicMWpAA"})],
+    )
+
+    requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_success()
+
+
+def test_oauth2_pkce_flow_uses_custom_failure(
+    token_cache, monkeypatch, browser_mock: BrowserMock
+):
+    monkeypatch.setattr(
+        requests_auth._oauth2.authorization_code_pkce.os, "urandom", lambda x: b"1" * 63
+    )
+    auth = requests_auth.OAuth2AuthorizationCodePKCE(
+        "http://provide_code",
+        "http://provide_access_token",
+    )
+    requests_auth.OAuth2.display.failure_html = "FAILURE: {display_time}\n{information}"
+    tab = browser_mock.add_response(
+        opened_url="http://provide_code?response_type=code&state=163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&code_challenge=5C_ph_KZ3DstYUc965SiqmKAA-ShvKF4Ut7daKd3fjc&code_challenge_method=S256",
+        reply_url="http://localhost:5000#error=invalid_request",
+        displayed_html="FAILURE: {display_time}\n{information}",
+    )
+
+    with pytest.raises(requests_auth.InvalidGrantRequest):
+        requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_failure(
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -146,9 +216,7 @@ def test_oauth2_pkce_flow_get_code_is_sent_in_authorization_header_by_default(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_flow_token_is_expired_after_30_seconds_by_default(
@@ -199,9 +267,7 @@ def test_oauth2_pkce_flow_token_is_expired_after_30_seconds_by_default(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_client_credentials_flow_token_custom_expiry(
@@ -270,9 +336,7 @@ def test_expires_in_sent_as_str(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_refresh_token(
@@ -316,9 +380,7 @@ def test_refresh_token(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
     # response for refresh token grant
     responses.post(
         "http://provide_access_token",
@@ -388,9 +450,7 @@ def test_refresh_token_invalid(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
     # response for refresh token grant
     responses.post(
         "http://provide_access_token",
@@ -421,9 +481,7 @@ def test_refresh_token_invalid(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_refresh_token_access_token_not_expired(
@@ -467,9 +525,7 @@ def test_refresh_token_access_token_not_expired(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
     # expect Bearer token to remain the same
     response = requests.get("http://authorized_only", auth=auth)
@@ -519,9 +575,7 @@ def test_nonce_is_sent_if_provided_in_authorization_url(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_no_json(
@@ -541,9 +595,7 @@ def test_with_invalid_grant_request_no_json(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "failure"
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error(
@@ -573,9 +625,7 @@ def test_with_invalid_grant_request_invalid_request_error(
         "includes multiple credentials, utilizes more than one mechanism for "
         "authenticating the client, or is otherwise malformed."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description(
@@ -599,9 +649,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc of the error"
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri(
@@ -632,9 +680,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on http://test_url"
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri_and_other_fields(
@@ -666,9 +712,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on http://test_url\nAdditional information: {{'other': 'other info'}}"
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_without_error(
@@ -692,9 +736,7 @@ def test_with_invalid_grant_request_without_error(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "{'other': 'other info'}"
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_client_error(
@@ -728,9 +770,7 @@ def test_with_invalid_grant_request_invalid_client_error(
         'code and include the "WWW-Authenticate" response header field matching the '
         "authentication scheme used by the client."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_grant_error(
@@ -760,9 +800,7 @@ def test_with_invalid_grant_request_invalid_grant_error(
         "does not match the redirection URI used in the authorization request, or was "
         "issued to another client."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unauthorized_client_error(
@@ -790,9 +828,7 @@ def test_with_invalid_grant_request_unauthorized_client_error(
         == "unauthorized_client: The authenticated client is not authorized to use this "
         "authorization grant type."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unsupported_grant_type_error(
@@ -820,9 +856,7 @@ def test_with_invalid_grant_request_unsupported_grant_type_error(
         == "unsupported_grant_type: The authorization grant type is not supported by the "
         "authorization server."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_scope_error(
@@ -850,9 +884,7 @@ def test_with_invalid_grant_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, malformed, or "
         "exceeds the scope granted by the resource owner."
     )
-    tab.assert_success(
-        "You are now authenticated on 163f0455b3e9cad3ca04254e5a0169553100d3aa0756c7964d897da316a695ffed5b4f46ef305094fd0a88cfe4b55ff257652015e4aa8f87b97513dba440f8de. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_token_request_invalid_request_error(
@@ -875,7 +907,7 @@ def test_with_invalid_token_request_invalid_request_error(
         == "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -895,9 +927,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc"
-    tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc"
-    )
+    tab.assert_failure("invalid_request: desc")
 
 
 def test_with_invalid_token_request_invalid_request_error_and_error_description_and_uri(
@@ -920,7 +950,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url"
+        "invalid_request: desc<br>More information can be found on http://test_url"
     )
 
 
@@ -944,7 +974,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
+        "invalid_request: desc<br>More information can be found on http://test_url<br>Additional information: {'other': ['test']}"
     )
 
 
@@ -968,7 +998,7 @@ def test_with_invalid_token_request_unauthorized_client_error(
         == "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
+        "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
 
 
@@ -992,7 +1022,7 @@ def test_with_invalid_token_request_access_denied_error(
         == "access_denied: The resource owner or authorization server denied the request."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: access_denied: The resource owner or authorization server denied the request."
+        "access_denied: The resource owner or authorization server denied the request."
     )
 
 
@@ -1016,7 +1046,7 @@ def test_with_invalid_token_request_unsupported_response_type_error(
         == "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
+        "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
 
 
@@ -1040,7 +1070,7 @@ def test_with_invalid_token_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_scope: The requested scope is invalid, unknown, or malformed."
+        "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
 
 
@@ -1064,7 +1094,7 @@ def test_with_invalid_token_request_server_error_error(
         == "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -1088,7 +1118,7 @@ def test_with_invalid_token_request_temporarily_unavailable_error(
         == "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -1135,9 +1165,7 @@ def test_response_type_can_be_provided_in_url(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on b32e05720bd3722e0ac87bf72897a78b669a0810adf8da46b675793dcfe0f41a40f7d7fdda952bd73ea533a2462907d805adf8c1a162d51b99b2ddec0d411feb. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_authorization_url_is_mandatory():
diff --git a/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce_okta.py b/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce_okta.py
index 1eb8eb3..e3e8634 100644
--- a/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce_okta.py
+++ b/tests/oauth2/authorization_code_pkce/test_oauth2_authorization_code_pkce_okta.py
@@ -56,9 +56,7 @@ def test_oauth2_pkce_flow_uses_provided_session(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_pkce_flow_uses_redirect_uri_domain(
@@ -106,8 +104,82 @@ def test_oauth2_pkce_flow_uses_redirect_uri_domain(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
+    tab.assert_success()
+
+
+def test_oauth2_pkce_flow_uses_custom_success(
+    token_cache, responses: RequestsMock, monkeypatch, browser_mock: BrowserMock
+):
+    monkeypatch.setattr(
+        requests_auth._oauth2.authorization_code_pkce.os, "urandom", lambda x: b"1" * 63
+    )
+    auth = requests_auth.OktaAuthorizationCodePKCE(
+        "testserver.okta-emea.com",
+        "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+    )
+    requests_auth.OAuth2.display.success_html = (
+        "<body><div>SUCCESS: {display_time}</div></body>"
+    )
+    tab = browser_mock.add_response(
+        opened_url="https://testserver.okta-emea.com/oauth2/default/v1/authorize?client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&code_challenge=5C_ph_KZ3DstYUc965SiqmKAA-ShvKF4Ut7daKd3fjc&code_challenge_method=S256",
+        reply_url="http://localhost:5000#code=SplxlOBeZQQYbYS6WxSbIA&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b",
+        displayed_html="<body><div>SUCCESS: {display_time}</div></body>",
+    )
+    responses.post(
+        "https://testserver.okta-emea.com/oauth2/default/v1/token",
+        json={
+            "access_token": "2YotnFZFEjr1zCsicMWpAA",
+            "token_type": "example",
+            "expires_in": 3600,
+            "refresh_token": "tGzv3JOkF0XG5Qx2TlKWIA",
+            "example_parameter": "example_value",
+        },
+        match=[
+            urlencoded_params_matcher(
+                {
+                    "code_verifier": "MTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTExMTEx",
+                    "grant_type": "authorization_code",
+                    "redirect_uri": "http://localhost:5000/",
+                    "client_id": "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+                    "scope": "openid",
+                    "response_type": "code",
+                    "code": "SplxlOBeZQQYbYS6WxSbIA",
+                }
+            ),
+        ],
+    )
+    responses.get(
+        "http://authorized_only",
+        match=[header_matcher({"Authorization": "Bearer 2YotnFZFEjr1zCsicMWpAA"})],
+    )
+
+    requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_success()
+
+
+def test_oauth2_pkce_flow_uses_custom_failure(
+    token_cache, monkeypatch, browser_mock: BrowserMock
+):
+    monkeypatch.setattr(
+        requests_auth._oauth2.authorization_code_pkce.os, "urandom", lambda x: b"1" * 63
+    )
+    auth = requests_auth.OktaAuthorizationCodePKCE(
+        "testserver.okta-emea.com",
+        "54239d18-c68c-4c47-8bdd-ce71ea1d50cd",
+    )
+    requests_auth.OAuth2.display.failure_html = "FAILURE: {display_time}\n{information}"
+    tab = browser_mock.add_response(
+        opened_url="https://testserver.okta-emea.com/oauth2/default/v1/authorize?client_id=54239d18-c68c-4c47-8bdd-ce71ea1d50cd&scope=openid&response_type=code&state=5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F&code_challenge=5C_ph_KZ3DstYUc965SiqmKAA-ShvKF4Ut7daKd3fjc&code_challenge_method=S256",
+        reply_url="http://localhost:5000#error=invalid_request",
+        displayed_html="FAILURE: {display_time}\n{information}",
+    )
+
+    with pytest.raises(requests_auth.InvalidGrantRequest):
+        requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_failure(
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -154,9 +226,7 @@ def test_oauth2_pkce_flow_get_code_is_sent_in_authorization_header_by_default(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_okta_pkce_flow_token_is_expired_after_30_seconds_by_default(
@@ -209,9 +279,7 @@ def test_okta_pkce_flow_token_is_expired_after_30_seconds_by_default(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_okta_pkce_flow_token_custom_expiry(
@@ -282,9 +350,7 @@ def test_expires_in_sent_as_str(
 
     requests.get("http://authorized_only", auth=auth)
 
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_no_json(
@@ -308,9 +374,7 @@ def test_with_invalid_grant_request_no_json(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "failure"
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error(
@@ -340,9 +404,7 @@ def test_with_invalid_grant_request_invalid_request_error(
         "includes multiple credentials, utilizes more than one mechanism for "
         "authenticating the client, or is otherwise malformed."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description(
@@ -366,9 +428,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc of the error"
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri(
@@ -399,9 +459,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on http://test_url"
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_request_error_and_error_description_and_uri_and_other_fields(
@@ -433,9 +491,7 @@ def test_with_invalid_grant_request_invalid_request_error_and_error_description_
         str(exception_info.value)
         == f"invalid_request: desc of the error\nMore information can be found on http://test_url\nAdditional information: {{'other': 'other info'}}"
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_without_error(
@@ -459,9 +515,7 @@ def test_with_invalid_grant_request_without_error(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "{'other': 'other info'}"
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_client_error(
@@ -495,9 +549,7 @@ def test_with_invalid_grant_request_invalid_client_error(
         'code and include the "WWW-Authenticate" response header field matching the '
         "authentication scheme used by the client."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_grant_error(
@@ -527,9 +579,7 @@ def test_with_invalid_grant_request_invalid_grant_error(
         "does not match the redirection URI used in the authorization request, or was "
         "issued to another client."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unauthorized_client_error(
@@ -557,9 +607,7 @@ def test_with_invalid_grant_request_unauthorized_client_error(
         == "unauthorized_client: The authenticated client is not authorized to use this "
         "authorization grant type."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_unsupported_grant_type_error(
@@ -587,9 +635,7 @@ def test_with_invalid_grant_request_unsupported_grant_type_error(
         == "unsupported_grant_type: The authorization grant type is not supported by the "
         "authorization server."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_grant_request_invalid_scope_error(
@@ -617,9 +663,7 @@ def test_with_invalid_grant_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, malformed, or "
         "exceeds the scope granted by the resource owner."
     )
-    tab.assert_success(
-        "You are now authenticated on 5264d11c8b268ccf911ce564ca42fd75cea68c4a3c1ec3ac1ab20243891ab7cd5250ad4c2d002017c6e8ac2ba34954293baa5e0e4fd00bb9ffd4a39c45f1960b. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_with_invalid_token_request_invalid_request_error(
@@ -642,7 +686,7 @@ def test_with_invalid_token_request_invalid_request_error(
         == "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -662,9 +706,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description(
     with pytest.raises(requests_auth.InvalidGrantRequest) as exception_info:
         requests.get("http://authorized_only", auth=auth)
     assert str(exception_info.value) == "invalid_request: desc"
-    tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc"
-    )
+    tab.assert_failure("invalid_request: desc")
 
 
 def test_with_invalid_token_request_invalid_request_error_and_error_description_and_uri(
@@ -687,7 +729,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url"
+        "invalid_request: desc<br>More information can be found on http://test_url"
     )
 
 
@@ -711,7 +753,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
+        "invalid_request: desc<br>More information can be found on http://test_url<br>Additional information: {'other': ['test']}"
     )
 
 
@@ -735,7 +777,7 @@ def test_with_invalid_token_request_unauthorized_client_error(
         == "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
+        "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
 
 
@@ -759,7 +801,7 @@ def test_with_invalid_token_request_access_denied_error(
         == "access_denied: The resource owner or authorization server denied the request."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: access_denied: The resource owner or authorization server denied the request."
+        "access_denied: The resource owner or authorization server denied the request."
     )
 
 
@@ -783,7 +825,7 @@ def test_with_invalid_token_request_unsupported_response_type_error(
         == "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
+        "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
 
 
@@ -807,7 +849,7 @@ def test_with_invalid_token_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_scope: The requested scope is invalid, unknown, or malformed."
+        "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
 
 
@@ -831,7 +873,7 @@ def test_with_invalid_token_request_server_error_error(
         == "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -855,7 +897,7 @@ def test_with_invalid_token_request_temporarily_unavailable_error(
         == "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
diff --git a/tests/oauth2/implicit/test_oauth2_implicit.py b/tests/oauth2/implicit/test_oauth2_implicit.py
index a19e619..abc23b3 100644
--- a/tests/oauth2/implicit/test_oauth2_implicit.py
+++ b/tests/oauth2/implicit/test_oauth2_implicit.py
@@ -72,12 +72,8 @@ def test_oauth2_implicit_flow_token_is_not_reused_if_a_url_parameter_is_changing
 
     requests.get("http://authorized_only", auth=auth2)
 
-    tab1.assert_success(
-        "You are now authenticated on 5652a8138e3a99dab7b94532c73ed5b10f19405316035d1efdc8bf7e0713690485254c2eaff912040eac44031889ef0a5ed5730c8a111541120d64a898c31afe. You may close this tab."
-    )
-    tab2.assert_success(
-        "You are now authenticated on 5c3940ccf78ac6e7d6d8d06782d9fd95a533aa5425b616eaa38dc3ec9508fbd55152c58a0d8dd8a087e76b77902559285819a41cb78ce8713e5a3b974bf07ce9. You may close this tab."
-    )
+    tab1.assert_success()
+    tab2.assert_success()
 
 
 def test_oauth2_implicit_flow_token_is_reused_if_only_nonce_differs(
@@ -113,9 +109,7 @@ def test_oauth2_implicit_flow_token_is_reused_if_only_nonce_differs(
     )
 
     requests.get("http://authorized_only", auth=auth2)
-    tab.assert_success(
-        "You are now authenticated on 67b95d2c7555751d1d72c97c7cd9ad6630c8395e0eaa51ee86ac7e451211ded9cd98a7190848789fe93632d8960425710e93f1f5549c6c6bc328bf3865a85ff2. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_token_can_be_requested_on_a_custom_server_port(
@@ -141,9 +135,7 @@ def test_oauth2_implicit_flow_token_can_be_requested_on_a_custom_server_port(
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_uses_redirect_uri_domain(
@@ -167,8 +159,51 @@ def test_oauth2_implicit_flow_uses_redirect_uri_domain(
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
+    tab.assert_success()
+
+
+def test_oauth2_implicit_flow_uses_custom_success(
+    token_cache, responses: RequestsMock, browser_mock: BrowserMock
+):
+    auth = requests_auth.OAuth2Implicit("http://provide_token")
+    requests_auth.OAuth2.display.success_html = (
+        "<body><div>SUCCESS: {display_time}</div></body>"
+    )
+    expiry_in_1_hour = datetime.datetime.now(
+        datetime.timezone.utc
+    ) + datetime.timedelta(hours=1)
+    token = create_token(expiry_in_1_hour)
+    tab = browser_mock.add_response(
+        opened_url="http://provide_token?response_type=token&state=42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000",
+        displayed_html="<body><div>SUCCESS: {display_time}</div></body>",
+        data=f"access_token={token}&state=42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521",
+    )
+    responses.get(
+        "http://authorized_only",
+        match=[header_matcher({"Authorization": f"Bearer {token}"})],
+    )
+
+    requests.get("http://authorized_only", auth=auth)
+    tab.assert_success()
+
+
+def test_oauth2_implicit_flow_uses_custom_failure(
+    token_cache, browser_mock: BrowserMock
+):
+    auth = requests_auth.OAuth2Implicit("http://provide_token")
+    requests_auth.OAuth2.display.failure_html = "FAILURE: {display_time}\n{information}"
+    tab = browser_mock.add_response(
+        opened_url="http://provide_token?response_type=token&state=42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521&redirect_uri=http%3A%2F%2Flocalhost%3A5000%2F",
+        reply_url="http://localhost:5000#error=invalid_request",
+        displayed_html="FAILURE: {display_time}\n{information}",
+    )
+
+    with pytest.raises(requests_auth.InvalidGrantRequest):
+        requests.get("http://authorized_only", auth=auth)
+
+    tab.assert_failure(
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -191,9 +226,7 @@ def test_oauth2_implicit_flow_post_token_is_sent_in_authorization_header_by_defa
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_token_is_expired_after_30_seconds_by_default(
@@ -225,9 +258,7 @@ def test_oauth2_implicit_flow_token_is_expired_after_30_seconds_by_default(
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_token_custom_expiry(
@@ -325,7 +356,7 @@ def test_state_change(token_cache, responses: RequestsMock, browser_mock: Browse
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success("You are now authenticated on 123456. You may close this tab.")
+    tab.assert_success()
 
 
 def test_empty_token_is_invalid(token_cache, browser_mock: BrowserMock):
@@ -340,9 +371,7 @@ def test_empty_token_is_invalid(token_cache, browser_mock: BrowserMock):
             auth=requests_auth.OAuth2Implicit("http://provide_token"),
         )
     assert str(exception_info.value) == " is invalid."
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_token_without_expiry_is_invalid(token_cache, browser_mock: BrowserMock):
@@ -357,9 +386,7 @@ def test_token_without_expiry_is_invalid(token_cache, browser_mock: BrowserMock)
             auth=requests_auth.OAuth2Implicit("http://provide_token"),
         )
     assert str(exception_info.value) == "Expiry (exp) is not provided in None."
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_get_token_is_sent_in_authorization_header_by_default(
@@ -380,9 +407,7 @@ def test_oauth2_implicit_flow_get_token_is_sent_in_authorization_header_by_defau
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_token_is_sent_in_requested_field(
@@ -406,9 +431,7 @@ def test_oauth2_implicit_flow_token_is_sent_in_requested_field(
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_can_send_a_custom_response_type_and_expects_token_to_be_received_with_this_name(
@@ -434,9 +457,7 @@ def test_oauth2_implicit_flow_can_send_a_custom_response_type_and_expects_token_
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 67b95d2c7555751d1d72c97c7cd9ad6630c8395e0eaa51ee86ac7e451211ded9cd98a7190848789fe93632d8960425710e93f1f5549c6c6bc328bf3865a85ff2. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_expects_token_in_id_token_if_response_type_is_id_token(
@@ -460,9 +481,7 @@ def test_oauth2_implicit_flow_expects_token_in_id_token_if_response_type_is_id_t
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 87c4108ec0eb03599335333a40434a36674269690b6957fef684bfb6c5a849ce660ef7031aa874c44d67cd3eada8febdfce41efb1ed3bc53a0a7e716cbba025a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_expects_token_in_id_token_if_response_type_in_url_is_id_token(
@@ -484,9 +503,7 @@ def test_oauth2_implicit_flow_expects_token_in_id_token_if_response_type_in_url_
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 87c4108ec0eb03599335333a40434a36674269690b6957fef684bfb6c5a849ce660ef7031aa874c44d67cd3eada8febdfce41efb1ed3bc53a0a7e716cbba025a. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_expects_token_to_be_stored_in_access_token_by_default(
@@ -508,9 +525,7 @@ def test_oauth2_implicit_flow_expects_token_to_be_stored_in_access_token_by_defa
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_token_is_reused_if_not_expired(
@@ -540,9 +555,7 @@ def test_oauth2_implicit_flow_token_is_reused_if_not_expired(
     )
 
     requests.get("http://authorized_only", auth=oauth2)
-    tab.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab.assert_success()
 
 
 def test_oauth2_implicit_flow_post_failure_if_token_is_not_provided(
@@ -559,9 +572,7 @@ def test_oauth2_implicit_flow_post_failure_if_token_is_not_provided(
             auth=requests_auth.OAuth2Implicit("http://provide_token"),
         )
     assert str(exception_info.value) == "access_token not provided within {}."
-    tab.assert_failure(
-        "Unable to properly perform authentication: access_token not provided within {}."
-    )
+    tab.assert_failure("access_token not provided within {}.")
 
 
 def test_oauth2_implicit_flow_get_failure_if_token_is_not_provided(
@@ -577,9 +588,7 @@ def test_oauth2_implicit_flow_get_failure_if_token_is_not_provided(
             auth=requests_auth.OAuth2Implicit("http://provide_token"),
         )
     assert str(exception_info.value) == "access_token not provided within {}."
-    tab.assert_failure(
-        "Unable to properly perform authentication: access_token not provided within {}."
-    )
+    tab.assert_failure("access_token not provided within {}.")
 
 
 def test_oauth2_implicit_flow_post_failure_if_state_is_not_provided(
@@ -603,9 +612,7 @@ def test_oauth2_implicit_flow_post_failure_if_state_is_not_provided(
         str(exception_info.value)
         == f"state not provided within {{'access_token': ['{token}']}}."
     )
-    tab.assert_failure(
-        f"Unable to properly perform authentication: state not provided within {{'access_token': ['{token}']}}."
-    )
+    tab.assert_failure(f"state not provided within {{'access_token': ['{token}']}}.")
 
 
 def test_oauth2_implicit_flow_get_failure_if_state_is_not_provided(
@@ -629,7 +636,7 @@ def test_oauth2_implicit_flow_get_failure_if_state_is_not_provided(
         == f"state not provided within {{'access_token': ['{token}'], 'requests_auth_redirect': ['1']}}."
     )
     tab.assert_failure(
-        f"Unable to properly perform authentication: state not provided within {{'access_token': ['{token}'], 'requests_auth_redirect': ['1']}}."
+        f"state not provided within {{'access_token': ['{token}'], 'requests_auth_redirect': ['1']}}."
     )
 
 
@@ -650,7 +657,7 @@ def test_with_invalid_token_request_invalid_request_error(
         == "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
+        "invalid_request: The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."
     )
 
 
@@ -667,9 +674,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description(
             auth=requests_auth.OAuth2Implicit("http://provide_token"),
         )
     assert str(exception_info.value) == "invalid_request: desc"
-    tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc"
-    )
+    tab.assert_failure("invalid_request: desc")
 
 
 def test_with_invalid_token_request_invalid_request_error_and_error_description_and_uri(
@@ -689,7 +694,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url"
+        "invalid_request: desc<br>More information can be found on http://test_url"
     )
 
 
@@ -710,7 +715,7 @@ def test_with_invalid_token_request_invalid_request_error_and_error_description_
         == "invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_request: desc\nMore information can be found on http://test_url\nAdditional information: {'other': ['test']}"
+        "invalid_request: desc<br>More information can be found on http://test_url<br>Additional information: {'other': ['test']}"
     )
 
 
@@ -731,7 +736,7 @@ def test_with_invalid_token_request_unauthorized_client_error(
         == "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
+        "unauthorized_client: The client is not authorized to request an authorization code or an access token using this method."
     )
 
 
@@ -752,7 +757,7 @@ def test_with_invalid_token_request_access_denied_error(
         == "access_denied: The resource owner or authorization server denied the request."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: access_denied: The resource owner or authorization server denied the request."
+        "access_denied: The resource owner or authorization server denied the request."
     )
 
 
@@ -773,7 +778,7 @@ def test_with_invalid_token_request_unsupported_response_type_error(
         == "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
+        "unsupported_response_type: The authorization server does not support obtaining an authorization code or an access token using this method."
     )
 
 
@@ -794,7 +799,7 @@ def test_with_invalid_token_request_invalid_scope_error(
         == "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: invalid_scope: The requested scope is invalid, unknown, or malformed."
+        "invalid_scope: The requested scope is invalid, unknown, or malformed."
     )
 
 
@@ -815,7 +820,7 @@ def test_with_invalid_token_request_server_error_error(
         == "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "server_error: The authorization server encountered an unexpected condition that prevented it from fulfilling the request. (This error code is needed because a 500 Internal Server Error HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -836,7 +841,7 @@ def test_with_invalid_token_request_temporarily_unavailable_error(
         == "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
     tab.assert_failure(
-        "Unable to properly perform authentication: temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
+        "temporarily_unavailable: The authorization server is currently unable to handle the request due to a temporary overloading or maintenance of the server.  (This error code is needed because a 503 Service Unavailable HTTP status code cannot be returned to the client via an HTTP redirect.)"
     )
 
 
@@ -899,9 +904,5 @@ def test_oauth2_implicit_flow_token_is_requested_again_if_expired(
     )
 
     requests.get("http://authorized_only", auth=auth)
-    tab1.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
-    tab2.assert_success(
-        "You are now authenticated on 42a85b271b7a652ca3cc4c398cfd3f01b9ad36bf9c945ba823b023e8f8b95c4638576a0e3dcc96838b838bec33ec6c0ee2609d62ed82480b3b8114ca494c0521. You may close this tab."
-    )
+    tab1.assert_success()
+    tab2.assert_success()