Support UI Authentication for OpenID Connect accounts (#7457)

synapse/handlers/oidc_handler.py

@@ -311,7 +311,7 @@ class OidcHandler:
         ``ClientAuth`` to authenticate with the client with its ID and secret.
 
         Args:
-            code: The autorization code we got from the callback.
+            code: The authorization code we got from the callback.
 
         Returns:
             A dict containing various tokens.
@@ -497,11 +497,14 @@ class OidcHandler:
         return UserInfo(claims)
 
     async def handle_redirect_request(
-        self, request: SynapseRequest, client_redirect_url: bytes
-    ) -> None:
+        self,
+        request: SynapseRequest,
+        client_redirect_url: bytes,
+        ui_auth_session_id: Optional[str] = None,
+    ) -> str:
         """Handle an incoming request to /login/sso/redirect
 
-        It redirects the browser to the authorization endpoint with a few
+        It returns a redirect to the authorization endpoint with a few
         parameters:
 
           - ``client_id``: the client ID set in ``oidc_config.client_id``
@@ -511,24 +514,32 @@ class OidcHandler:
           - ``state``: a random string
           - ``nonce``: a random string
 
-        In addition to redirecting the client, we are setting a cookie with
+        In addition generating a redirect URL, we are setting a cookie with
         a signed macaroon token containing the state, the nonce and the
         client_redirect_url params. Those are then checked when the client
         comes back from the provider.
 
-
         Args:
             request: the incoming request from the browser.
                 We'll respond to it with a redirect and a cookie.
             client_redirect_url: the URL that we should redirect the client to
                 when everything is done
+            ui_auth_session_id: The session ID of the ongoing UI Auth (or
+                None if this is a login).
+
+        Returns:
+            The redirect URL to the authorization endpoint.
+
         """
 
         state = generate_token()
         nonce = generate_token()
 
         cookie = self._generate_oidc_session_token(
-            state=state, nonce=nonce, client_redirect_url=client_redirect_url.decode(),
+            state=state,
+            nonce=nonce,
+            client_redirect_url=client_redirect_url.decode(),
+            ui_auth_session_id=ui_auth_session_id,
         )
         request.addCookie(
             SESSION_COOKIE_NAME,
@@ -541,7 +552,7 @@ class OidcHandler:
 
         metadata = await self.load_metadata()
         authorization_endpoint = metadata.get("authorization_endpoint")
-        uri = prepare_grant_uri(
+        return prepare_grant_uri(
             authorization_endpoint,
             client_id=self._client_auth.client_id,
             response_type="code",
@@ -550,8 +561,6 @@ class OidcHandler:
             state=state,
             nonce=nonce,
         )
-        request.redirect(uri)
-        finish_request(request)
 
     async def handle_oidc_callback(self, request: SynapseRequest) -> None:
         """Handle an incoming request to /_synapse/oidc/callback
@@ -625,7 +634,11 @@ class OidcHandler:
 
         # Deserialize the session token and verify it.
         try:
-            nonce, client_redirect_url = self._verify_oidc_session_token(session, state)
+            (
+                nonce,
+                client_redirect_url,
+                ui_auth_session_id,
+            ) = self._verify_oidc_session_token(session, state)
         except MacaroonDeserializationException as e:
             logger.exception("Invalid session")
             self._render_error(request, "invalid_session", str(e))
@@ -678,15 +691,21 @@ class OidcHandler:
             return
 
         # and finally complete the login
-        await self._auth_handler.complete_sso_login(
-            user_id, request, client_redirect_url
-        )
+        if ui_auth_session_id:
+            await self._auth_handler.complete_sso_ui_auth(
+                user_id, ui_auth_session_id, request
+            )
+        else:
+            await self._auth_handler.complete_sso_login(
+                user_id, request, client_redirect_url
+            )
 
     def _generate_oidc_session_token(
         self,
         state: str,
         nonce: str,
         client_redirect_url: str,
+        ui_auth_session_id: Optional[str],
         duration_in_ms: int = (60 * 60 * 1000),
     ) -> str:
         """Generates a signed token storing data about an OIDC session.
@@ -702,6 +721,8 @@ class OidcHandler:
             nonce: The ``nonce`` parameter passed to the OIDC provider.
             client_redirect_url: The URL the client gave when it initiated the
                 flow.
+            ui_auth_session_id: The session ID of the ongoing UI Auth (or
+                None if this is a login).
             duration_in_ms: An optional duration for the token in milliseconds.
                 Defaults to an hour.
 
@@ -718,12 +739,19 @@ class OidcHandler:
         macaroon.add_first_party_caveat(
             "client_redirect_url = %s" % (client_redirect_url,)
         )
+        if ui_auth_session_id:
+            macaroon.add_first_party_caveat(
+                "ui_auth_session_id = %s" % (ui_auth_session_id,)
+            )
         now = self._clock.time_msec()
         expiry = now + duration_in_ms
         macaroon.add_first_party_caveat("time < %d" % (expiry,))
+
         return macaroon.serialize()
 
-    def _verify_oidc_session_token(self, session: str, state: str) -> Tuple[str, str]:
+    def _verify_oidc_session_token(
+        self, session: str, state: str
+    ) -> Tuple[str, str, Optional[str]]:
         """Verifies and extract an OIDC session token.
 
         This verifies that a given session token was issued by this homeserver
@@ -734,7 +762,7 @@ class OidcHandler:
             state: The state the OIDC provider gave back
 
         Returns:
-            The nonce and the client_redirect_url for this session
+            The nonce, client_redirect_url, and ui_auth_session_id for this session
         """
         macaroon = pymacaroons.Macaroon.deserialize(session)
 
@@ -744,17 +772,27 @@ class OidcHandler:
         v.satisfy_exact("state = %s" % (state,))
         v.satisfy_general(lambda c: c.startswith("nonce = "))
         v.satisfy_general(lambda c: c.startswith("client_redirect_url = "))
+        # Sometimes there's a UI auth session ID, it seems to be OK to attempt
+        # to always satisfy this.
+        v.satisfy_general(lambda c: c.startswith("ui_auth_session_id = "))
         v.satisfy_general(self._verify_expiry)
 
         v.verify(macaroon, self._macaroon_secret_key)
 
-        # Extract the `nonce` and `client_redirect_url` from the token
+        # Extract the `nonce`, `client_redirect_url`, and maybe the
+        # `ui_auth_session_id` from the token.
         nonce = self._get_value_from_macaroon(macaroon, "nonce")
         client_redirect_url = self._get_value_from_macaroon(
             macaroon, "client_redirect_url"
         )
+        try:
+            ui_auth_session_id = self._get_value_from_macaroon(
+                macaroon, "ui_auth_session_id"
+            )  # type: Optional[str]
+        except ValueError:
+            ui_auth_session_id = None
 
-        return nonce, client_redirect_url
+        return nonce, client_redirect_url, ui_auth_session_id
 
     def _get_value_from_macaroon(self, macaroon: pymacaroons.Macaroon, key: str) -> str:
         """Extracts a caveat value from a macaroon token.
@@ -773,7 +811,7 @@ class OidcHandler:
         for caveat in macaroon.caveats:
             if caveat.caveat_id.startswith(prefix):
                 return caveat.caveat_id[len(prefix) :]
-        raise Exception("No %s caveat in macaroon" % (key,))
+        raise ValueError("No %s caveat in macaroon" % (key,))
 
     def _verify_expiry(self, caveat: str) -> bool:
         prefix = "time < "