fix: handle URL-safe base64 decoding for JWT (#38991)

* fix: handle URL-safe base64 decoding for JWT

- Updated the JWT decoding logic to use URL-safe base64 decoding.
- Added padding to the base64 encoded string to ensure proper decoding.
- This fixes the issue where UTF-8 decoding errors occurred due to missing padding in the base64 string.

Changes:
- Replaced `base64.decodebytes` with `base64.urlsafe_b64decode`.
- Added logic to calculate and append necessary padding to the base64 string.

* More concise way as requested

* Extend changes to aio decorators.py as requested

* format by black

* Update sdk/identity/azure-identity/azure/identity/_internal/decorators.py

Co-authored-by: Paul Van Eck <paulvaneck@microsoft.com>

* Update sdk/identity/azure-identity/azure/identity/aio/_internal/decorators.py

Co-authored-by: Paul Van Eck <paulvaneck@microsoft.com>

* Formatted code using Black as specified in ../../../eng/tox/tox.ini with the designated version

---------

Co-authored-by: Paul Van Eck <paulvaneck@microsoft.com>

sdk/identity/azure-identity/azure/identity/_internal/decorators.py

@@ -22,12 +22,17 @@ def wrapper(*args, **kwargs):
         try:
             token = fn(*args, **kwargs)
             _LOGGER.log(
-                logging.DEBUG if within_credential_chain.get() else logging.INFO, "%s succeeded", fn.__qualname__
+                logging.DEBUG if within_credential_chain.get() else logging.INFO,
+                "%s succeeded",
+                fn.__qualname__,
             )
             if _LOGGER.isEnabledFor(logging.DEBUG):
                 try:
-                    base64_meta_data = token.token.split(".")[1].encode("utf-8") + b"=="
-                    json_bytes = base64.decodebytes(base64_meta_data)
+                    base64_meta_data = token.token.split(".")[1]
+                    padding_needed = -len(base64_meta_data) % 4
+                    if padding_needed:
+                        base64_meta_data += "=" * padding_needed
+                    json_bytes = base64.urlsafe_b64decode(base64_meta_data)
                     json_string = json_bytes.decode("utf-8")
                     json_dict = json.loads(json_string)
                     upn = json_dict.get("upn", "unavailableUpn")

sdk/identity/azure-identity/azure/identity/aio/_internal/decorators.py

@@ -21,12 +21,17 @@ async def wrapper(*args, **kwargs):
         try:
             token = await fn(*args, **kwargs)
             _LOGGER.log(
-                logging.DEBUG if within_credential_chain.get() else logging.INFO, "%s succeeded", fn.__qualname__
+                logging.DEBUG if within_credential_chain.get() else logging.INFO,
+                "%s succeeded",
+                fn.__qualname__,
             )
             if _LOGGER.isEnabledFor(logging.DEBUG):
                 try:
-                    base64_meta_data = token.token.split(".")[1].encode("utf-8") + b"=="
-                    json_bytes = base64.decodebytes(base64_meta_data)
+                    base64_meta_data = token.token.split(".")[1]
+                    padding_needed = -len(base64_meta_data) % 4
+                    if padding_needed:
+                        base64_meta_data += "=" * padding_needed
+                    json_bytes = base64.urlsafe_b64decode(base64_meta_data)
                     json_string = json_bytes.decode("utf-8")
                     json_dict = json.loads(json_string)
                     upn = json_dict.get("upn", "unavailableUpn")