Clean up exception handling in SAML2ResponseResource (#7614)

* Expose `return_html_error`, and allow it to take a Jinja2 template instead of a raw string

* Clean up exception handling in SAML2ResponseResource

  * use the existing code in `return_html_error` instead of re-implementing it
    (giving it a jinja2 template rather than inventing a new form of template)

  * do the exception-catching in the REST layer rather than in the handler
    layer, to make sure we catch all exceptions.

1 files changed, 13 insertions, 13 deletions

diff --git a/synapse/rest/saml2/response_resource.py b/synapse/rest/saml2/response_resource.py
index a545c13db7..75e58043b4 100644
--- a/synapse/rest/saml2/response_resource.py
+++ b/synapse/rest/saml2/response_resource.py
@@ -13,12 +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,
-    finish_request,
-    wrap_html_request_handler,
-)
+from synapse.api.errors import SynapseError
+from synapse.http.server import DirectServeResource, return_html_error
 
 
 class SAML2ResponseResource(DirectServeResource):
@@ -28,20 +26,22 @@ class SAML2ResponseResource(DirectServeResource):
 
     def __init__(self, hs):
         super().__init__()
-        self._error_html_content = hs.config.saml2_error_html_content
         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.
-        request.setResponseCode(400)
-        request.setHeader(b"Content-Type", b"text/html; charset=utf-8")
-        request.setHeader(b"Content-Length", b"%d" % (len(self._error_html_content),))
-        request.write(self._error_html_content.encode("utf8"))
-        finish_request(request)
+        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)