1 files changed, 19 insertions, 3 deletions
diff --git a/synapse/rest/saml2/response_resource.py b/synapse/rest/saml2/response_resource.py
index 69ecc5e4b4..75e58043b4 100644
--- a/synapse/rest/saml2/response_resource.py
+++ b/synapse/rest/saml2/response_resource.py
@@ -13,8 +13,10 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from twisted.python import failure
 
-from synapse.http.server import DirectServeResource, wrap_html_request_handler
+from synapse.api.errors import SynapseError
+from synapse.http.server import DirectServeResource, return_html_error
 
 
 class SAML2ResponseResource(DirectServeResource):
@@ -25,7 +27,21 @@ class SAML2ResponseResource(DirectServeResource):
     def __init__(self, hs):
         super().__init__()
         self._saml_handler = hs.get_saml_handler()
+        self._error_html_template = hs.config.saml2.saml2_error_html_template
+
+    async def _async_render_GET(self, request):
+        # We're not expecting any GET request on that resource if everything goes right,
+        # but some IdPs sometimes end up responding with a 302 redirect on this endpoint.
+        # In this case, just tell the user that something went wrong and they should
+        # try to authenticate again.
+        f = failure.Failure(
+            SynapseError(400, "Unexpected GET request on /saml2/authn_response")
+        )
+        return_html_error(f, request, self._error_html_template)
 
-    @wrap_html_request_handler
     async def _async_render_POST(self, request):
-        return await self._saml_handler.handle_saml_response(request)
+        try:
+            await self._saml_handler.handle_saml_response(request)
+        except Exception:
+            f = failure.Failure()
+            return_html_error(f, request, self._error_html_template)