diff --git a/credential-management/support/fedcm/manifest-not-in-list.json b/credential-management/support/fedcm/manifest-not-in-list.json
index c66903cfd22d8ff..b6d8a5541b7c0fe 100644
--- a/credential-management/support/fedcm/manifest-not-in-list.json
+++ b/credential-management/support/fedcm/manifest-not-in-list.json
@@ -1,5 +1,6 @@
 {
   "accounts_endpoint": "accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
-  "id_assertion_endpoint": "token.py"
+  "id_assertion_endpoint": "token.py",
+  "signin_url": "signin.html"
 }
diff --git a/credential-management/support/fedcm/manifest.py b/credential-management/support/fedcm/manifest.py
index 8a6172ce161aec4..5a6166fded5f2c9 100644
--- a/credential-management/support/fedcm/manifest.py
+++ b/credential-management/support/fedcm/manifest.py
@@ -13,6 +13,7 @@ def main(request, response):
   "accounts_endpoint": "accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
   "id_assertion_endpoint": "token.py",
-  "revocation_endpoint": "revoke.py"
+  "revocation_endpoint": "revoke.py",
+  "signin_url": "signin.html"
 }
 """
diff --git a/credential-management/support/fedcm/manifest_redirect_accounts.json b/credential-management/support/fedcm/manifest_redirect_accounts.json
index 590704cfeb169d5..5aec07f40c84b4a 100644
--- a/credential-management/support/fedcm/manifest_redirect_accounts.json
+++ b/credential-management/support/fedcm/manifest_redirect_accounts.json
@@ -1,5 +1,6 @@
 {
   "accounts_endpoint": "/common/redirect.py?location=/credential-management/support/fedcm/accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
-  "id_assertion_endpoint": "token.py"
+  "id_assertion_endpoint": "token.py",
+  "signin_url": "signin.html"
 }
diff --git a/credential-management/support/fedcm/manifest_redirect_token.json b/credential-management/support/fedcm/manifest_redirect_token.json
index 190420736dfbd6a..84800884de3e44c 100644
--- a/credential-management/support/fedcm/manifest_redirect_token.json
+++ b/credential-management/support/fedcm/manifest_redirect_token.json
@@ -2,5 +2,6 @@
   "accounts_endpoint": "accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
   "id_assertion_endpoint": "/common/redirect.py?location=/credential-management/support/fedcm/token.py&status=308",
-  "revocation_endpoint": "revoke.py"
+  "revocation_endpoint": "revoke.py",
+  "signin_url": "signin.html"
 }
diff --git a/credential-management/support/fedcm/manifest_with_account_auto_selected_flag.json b/credential-management/support/fedcm/manifest_with_account_auto_selected_flag.json
index 39d2b1eec88c58c..20ee0bf429f6703 100644
--- a/credential-management/support/fedcm/manifest_with_account_auto_selected_flag.json
+++ b/credential-management/support/fedcm/manifest_with_account_auto_selected_flag.json
@@ -1,5 +1,6 @@
 {
   "accounts_endpoint": "two_accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
-  "id_assertion_endpoint": "token_with_account_auto_selected_flag.py"
+  "id_assertion_endpoint": "token_with_account_auto_selected_flag.py",
+  "signin_url": "signin.html"
 }
diff --git a/credential-management/support/fedcm/manifest_with_no_accounts.json b/credential-management/support/fedcm/manifest_with_no_accounts.json
index ad3f295ea8543a9..3667eae23ae504e 100644
--- a/credential-management/support/fedcm/manifest_with_no_accounts.json
+++ b/credential-management/support/fedcm/manifest_with_no_accounts.json
@@ -1,5 +1,6 @@
 {
   "accounts_endpoint": "no_accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
-  "id_assertion_endpoint": "token_with_account_id.py"
+  "id_assertion_endpoint": "token_with_account_id.py",
+  "signin_url": "signin.html"
 }
diff --git a/credential-management/support/fedcm/manifest_with_single_account.json b/credential-management/support/fedcm/manifest_with_single_account.json
index 15a657c679df7b0..d1eb008c70d4771 100644
--- a/credential-management/support/fedcm/manifest_with_single_account.json
+++ b/credential-management/support/fedcm/manifest_with_single_account.json
@@ -1,5 +1,6 @@
 {
   "accounts_endpoint": "single_account.py",
   "client_metadata_endpoint": "client_metadata.py",
-  "id_assertion_endpoint": "token_with_account_id.py"
+  "id_assertion_endpoint": "token_with_account_id.py",
+  "signin_url": "signin.html"
 }
diff --git a/credential-management/support/fedcm/manifest_with_two_accounts.json b/credential-management/support/fedcm/manifest_with_two_accounts.json
index 932fb85dac34646..2a93b2f8afbbaf8 100644
--- a/credential-management/support/fedcm/manifest_with_two_accounts.json
+++ b/credential-management/support/fedcm/manifest_with_two_accounts.json
@@ -1,5 +1,6 @@
 {
   "accounts_endpoint": "two_accounts.py",
   "client_metadata_endpoint": "client_metadata.py",
-  "id_assertion_endpoint": "token_with_account_id.py"
+  "id_assertion_endpoint": "token_with_account_id.py",
+  "signin_url": "signin.html"
 }