matrix-org · clokep · Aug 18, 2021 · Aug 5, 2021 · Aug 11, 2021 · Aug 11, 2021
@@ -0,0 +1 @@
+Handle failure of User-Interactive Authentication when using a fallback. Contributed by Callum Brown.
@@ -627,23 +627,28 @@ async def check_ui_auth(
 
     async def add_oob_auth(
         self, stagetype: str, authdict: Dict[str, Any], clientip: str
-    ) -> bool:
+    ) -> None:
         """
         Adds the result of out-of-band authentication into an existing auth
         session. Currently used for adding the result of fallback auth.
+
+        Raises:
+            LoginError if the stagetype is unknown or the session is missing.
+            LoginError is raised by check_auth if authentication fails.
         """
         if stagetype not in self.checkers:
-            raise LoginError(400, "", Codes.MISSING_PARAM)
+            raise LoginError(
+                400, f"Unknown UIA stage type: {stagetype}", Codes.INVALID_PARAM
+            )
         if "session" not in authdict:
-            raise LoginError(400, "", Codes.MISSING_PARAM)
+            raise LoginError(400, "Missing session ID", Codes.MISSING_PARAM)
 
+        # If authentication fails a LoginError is raised. Otherwise, store
+        # the successful result.
         result = await self.checkers[stagetype].check_auth(authdict, clientip)
-        if result:
-            await self.store.mark_ui_auth_stage_complete(
-                authdict["session"], stagetype, result
-            )
-            return True
-        return False
+        await self.store.mark_ui_auth_stage_complete(
+            authdict["session"], stagetype, result
+        )
 
     def get_session_id(self, clientdict: Dict[str, Any]) -> Optional[str]:
         """

@@ -49,7 +49,7 @@ async def check_auth(self, authdict: dict, clientip: str) -> Any:
             clientip: The IP address of the client.
 
         Raises:
-            SynapseError if authentication failed
+            LoginError if authentication failed.
 
         Returns:
             The result of authentication (to pass back to the client?)

@@ -16,6 +16,9 @@
 <body>
 <form id="registrationForm" method="post" action="{{ myurl }}">
     <div>
+        {% if error is defined %}
+            <p class="error"><strong>Error: {{ error }}</strong></p>
+        {% endif %}
         <p>
         Hello! We need to prevent computer programs and other automated
         things from creating accounts on this server.

@@ -8,6 +8,9 @@
 <body>
 <form id="registrationForm" method="post" action="{{ myurl }}">
     <div>
+        {% if error is defined %}
+            <p class="error"><strong>Error: {{ error }}</strong></p>
+        {% endif %}
         <p>
             Please click the button below if you agree to the
             <a href="{{ terms_url }}">privacy policy of this homeserver.</a>

diff --git a/synapse/rest/client/v2_alpha/auth.py b/synapse/rest/client/v2_alpha/auth.py
@@ -16,7 +16,7 @@
 from typing import TYPE_CHECKING
 
 from synapse.api.constants import LoginType
-from synapse.api.errors import SynapseError
+from synapse.api.errors import LoginError, SynapseError
 from synapse.api.urls import CLIENT_API_PREFIX
 from synapse.http.server import respond_with_html
 from synapse.http.servlet import RestServlet, parse_string
@@ -95,29 +95,32 @@ async def on_POST(self, request, stagetype):
 
             authdict = {"response": response, "session": session}
 
-            success = await self.auth_handler.add_oob_auth(
-                LoginType.RECAPTCHA, authdict, request.getClientIP()
-            )
-
-            if success:
-                html = self.success_template.render()
-            else:
+            try:
+                await self.auth_handler.add_oob_auth(
+                    LoginType.RECAPTCHA, authdict, request.getClientIP()
+                )
+            except LoginError as e:
+                # Authentication failed, let user try again
                 html = self.recaptcha_template.render(
                     session=session,
                     myurl="%s/r0/auth/%s/fallback/web"
                     % (CLIENT_API_PREFIX, LoginType.RECAPTCHA),
                     sitekey=self.hs.config.recaptcha_public_key,
+                    error=e.msg,
                 )
+            else:
+                # No LoginError was raised, so authentication was successful
+                html = self.success_template.render()
+
         elif stagetype == LoginType.TERMS:
             authdict = {"session": session}
 
-            success = await self.auth_handler.add_oob_auth(
-                LoginType.TERMS, authdict, request.getClientIP()
-            )
-
-            if success:
-                html = self.success_template.render()
-            else:
+            try:
+                await self.auth_handler.add_oob_auth(
+                    LoginType.TERMS, authdict, request.getClientIP()
+                )
+            except LoginError as e:
+                # Authentication failed, let user try again
                 html = self.terms_template.render(
                     session=session,
                     terms_url="%s_matrix/consent?v=%s"
@@ -127,10 +130,16 @@ async def on_POST(self, request, stagetype):
                     ),
                     myurl="%s/r0/auth/%s/fallback/web"
                     % (CLIENT_API_PREFIX, LoginType.TERMS),
+                    error=e.msg,
                 )
+            else:
+                # No LoginError was raised, so authentication was successful
+                html = self.success_template.render()
+
         elif stagetype == LoginType.SSO:
             # The SSO fallback workflow should not post here,
             raise SynapseError(404, "Fallback SSO auth does not support POST requests.")
+
         else:
             raise SynapseError(404, "Unknown auth stage type")
 

@@ -57,4 +57,8 @@ textarea, input {
 
     background-color: #f8f8f8;
     border: 1px #ccc solid;
-}
+}
+
+.error {
+	color: red;
+}