Merge pull request #9091 from matrix-org/rav/error_on_bad_sso

Give the user a better error when they present bad SSO creds

4 files changed, 67 insertions, 31 deletions

diff --git a/synapse/config/sso.py b/synapse/config/sso.py
index 1aeb1c5c92..366f0d4698 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -37,6 +37,7 @@ class SSOConfig(Config):
             self.sso_error_template,
             sso_account_deactivated_template,
             sso_auth_success_template,
+            self.sso_auth_bad_user_template,
         ) = self.read_templates(
             [
                 "sso_login_idp_picker.html",
@@ -45,6 +46,7 @@ class SSOConfig(Config):
                 "sso_error.html",
                 "sso_account_deactivated.html",
                 "sso_auth_success.html",
+                "sso_auth_bad_user.html",
             ],
             template_dir,
         )
@@ -160,6 +162,14 @@ class SSOConfig(Config):
             #
             #   This template has no additional variables.
             #
+            # * HTML page shown after a user-interactive authentication session which
+            #   does not map correctly onto the expected user: 'sso_auth_bad_user.html'.
+            #
+            #   When rendering, this template is given the following variables:
+            #     * server_name: the homeserver's name.
+            #     * user_id_to_verify: the MXID of the user that we are trying to
+            #       validate.
+            #
             # * HTML page shown during single sign-on if a deactivated user (according to Synapse's database)
             #   attempts to login: 'sso_account_deactivated.html'.
             #
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 4f881a439a..18cd2b62f0 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -263,10 +263,6 @@ class AuthHandler(BaseHandler):
         # authenticating for an operation to occur on their account.
         self._sso_auth_confirm_template = hs.config.sso_auth_confirm_template
 
-        # The following template is shown after a successful user interactive
-        # authentication session. It tells the user they can close the window.
-        self._sso_auth_success_template = hs.config.sso_auth_success_template
-
         # The following template is shown during the SSO authentication process if
         # the account is deactivated.
         self._sso_account_deactivated_template = (
@@ -1394,27 +1390,6 @@ class AuthHandler(BaseHandler):
             description=session.description, redirect_url=redirect_url,
         )
 
-    async def complete_sso_ui_auth(
-        self, registered_user_id: str, session_id: str, request: Request,
-    ):
-        """Having figured out a mxid for this user, complete the HTTP request
-
-        Args:
-            registered_user_id: The registered user ID to complete SSO login for.
-            session_id: The ID of the user-interactive auth session.
-            request: The request to complete.
-        """
-        # Mark the stage of the authentication as successful.
-        # Save the user who authenticated with SSO, this will be used to ensure
-        # that the account be modified is also the person who logged in.
-        await self.store.mark_ui_auth_stage_complete(
-            session_id, LoginType.SSO, registered_user_id
-        )
-
-        # Render the HTML and return.
-        html = self._sso_auth_success_template
-        respond_with_html(request, 200, html)
-
     async def complete_sso_login(
         self,
         registered_user_id: str,
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index d096e0b091..dcc85e9871 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -22,7 +22,9 @@ from typing_extensions import NoReturn, Protocol
 
 from twisted.web.http import Request
 
+from synapse.api.constants import LoginType
 from synapse.api.errors import Codes, RedirectException, SynapseError
+from synapse.handlers.ui_auth import UIAuthSessionDataConstants
 from synapse.http import get_request_user_agent
 from synapse.http.server import respond_with_html
 from synapse.http.site import SynapseRequest
@@ -146,8 +148,13 @@ class SsoHandler:
         self._store = hs.get_datastore()
         self._server_name = hs.hostname
         self._registration_handler = hs.get_registration_handler()
-        self._error_template = hs.config.sso_error_template
         self._auth_handler = hs.get_auth_handler()
+        self._error_template = hs.config.sso_error_template
+        self._bad_user_template = hs.config.sso_auth_bad_user_template
+
+        # The following template is shown after a successful user interactive
+        # authentication session. It tells the user they can close the window.
+        self._sso_auth_success_template = hs.config.sso_auth_success_template
 
         # a lock on the mappings
         self._mapping_lock = Linearizer(name="sso_user_mapping", clock=hs.get_clock())
@@ -577,19 +584,45 @@ class SsoHandler:
             auth_provider_id, remote_user_id,
         )
 
+        user_id_to_verify = await self._auth_handler.get_session_data(
+            ui_auth_session_id, UIAuthSessionDataConstants.REQUEST_USER_ID
+        )  # type: str
+
         if not user_id:
             logger.warning(
                 "Remote user %s/%s has not previously logged in here: UIA will fail",
                 auth_provider_id,
                 remote_user_id,
             )
-            # Let the UIA flow handle this the same as if they presented creds for a
-            # different user.
-            user_id = ""
+        elif user_id != user_id_to_verify:
+            logger.warning(
+                "Remote user %s/%s mapped onto incorrect user %s: UIA will fail",
+                auth_provider_id,
+                remote_user_id,
+                user_id,
+            )
+        else:
+            # success!
+            # Mark the stage of the authentication as successful.
+            await self._store.mark_ui_auth_stage_complete(
+                ui_auth_session_id, LoginType.SSO, user_id
+            )
+
+            # Render the HTML confirmation page and return.
+            html = self._sso_auth_success_template
+            respond_with_html(request, 200, html)
+            return
+
+        # the user_id didn't match: mark the stage of the authentication as unsuccessful
+        await self._store.mark_ui_auth_stage_complete(
+            ui_auth_session_id, LoginType.SSO, ""
+        )
 
-        await self._auth_handler.complete_sso_ui_auth(
-            user_id, ui_auth_session_id, request
+        # render an error page.
+        html = self._bad_user_template.render(
+            server_name=self._server_name, user_id_to_verify=user_id_to_verify,
         )
+        respond_with_html(request, 200, html)
 
     async def check_username_availability(
         self, localpart: str, session_id: str,
diff --git a/synapse/res/templates/sso_auth_bad_user.html b/synapse/res/templates/sso_auth_bad_user.html
new file mode 100644
index 0000000000..3611191bf9
--- /dev/null
+++ b/synapse/res/templates/sso_auth_bad_user.html
@@ -0,0 +1,18 @@
+<html>
+<head>
+    <title>Authentication Failed</title>
+</head>
+    <body>
+        <div>
+            <p>
+                We were unable to validate your <tt>{{server_name | e}}</tt> account via
+                single-sign-on (SSO), because the SSO Identity Provider returned
+                different details than when you logged in.
+            </p>
+            <p>
+                Try the operation again, and ensure that you use the same details on
+                the Identity Provider as when you log into your account.
+            </p>
+        </div>
+    </body>
+</html>