Revert "Merge pull request #7153 from matrix-org/babolivier/sso_whitelist_login_fallback"

This was incorrectly merged to master.

This reverts commit 319c41f573eb14a966367b60b2e6e93bf6b028d9, reversing
changes made to 229eb81498b0fe1da81e9b5b333a0285acde9446.

changelog.d/7153.feature

@@ -1 +0,0 @@
-Always whitelist the login fallback in the SSO configuration if `public_baseurl` is set.

docs/sample_config.yaml

@@ -1392,10 +1392,6 @@ sso:
     # phishing attacks from evil.site. To avoid this, include a slash after the
     # hostname: "https://my.client/".
     #
-    # If public_baseurl is set, then the login fallback page (used by clients
-    # that don't natively support the required login flows) is whitelisted in
-    # addition to any URLs in this list.
-    #
     # By default, this list is empty.
     #
     #client_whitelist:

synapse/config/sso.py

@@ -39,17 +39,6 @@ class SSOConfig(Config):
 
         self.sso_client_whitelist = sso_config.get("client_whitelist") or []
 
-        # Attempt to also whitelist the server's login fallback, since that fallback sets
-        # the redirect URL to itself (so it can process the login token then return
-        # gracefully to the client). This would make it pointless to ask the user for
-        # confirmation, since the URL the confirmation page would be showing wouldn't be
-        # the client's.
-        # public_baseurl is an optional setting, so we only add the fallback's URL to the
-        # list if it's provided (because we can't figure out what that URL is otherwise).
-        if self.public_baseurl:
-            login_fallback_url = self.public_baseurl + "_matrix/static/client/login"
-            self.sso_client_whitelist.append(login_fallback_url)
-
     def generate_config_section(self, **kwargs):
         return """\
         # Additional settings to use with single-sign on systems such as SAML2 and CAS.
@@ -65,10 +54,6 @@ class SSOConfig(Config):
             # phishing attacks from evil.site. To avoid this, include a slash after the
             # hostname: "https://my.client/".
             #
-            # If public_baseurl is set, then the login fallback page (used by clients
-            # that don't natively support the required login flows) is whitelisted in
-            # addition to any URLs in this list.
-            #
             # By default, this list is empty.
             #
             #client_whitelist:

tests/rest/client/v1/test_login.py

@@ -350,14 +350,7 @@ class CASRedirectConfirmTestCase(unittest.HomeserverTestCase):
     def test_cas_redirect_whitelisted(self):
         """Tests that the SSO login flow serves a redirect to a whitelisted url
         """
-        self._test_redirect("https://legit-site.com/")
-
-    @override_config({"public_baseurl": "https://example.com"})
-    def test_cas_redirect_login_fallback(self):
-        self._test_redirect("https://example.com/_matrix/static/client/login")
-
-    def _test_redirect(self, redirect_url):
-        """Tests that the SSO login flow serves a redirect for the given redirect URL."""
+        redirect_url = "https://legit-site.com/"
         cas_ticket_url = (
             "/_matrix/client/r0/login/cas/ticket?redirectUrl=%s&ticket=ticket"
             % (urllib.parse.quote(redirect_url))