Log more detail when we fail to authenticate request

synapse/federation/transport/server.py

@@ -261,10 +261,10 @@ class BaseFederationServlet(object):
             except NoAuthenticationError:
                 origin = None
                 if self.REQUIRE_AUTH:
-                    logger.warn("authenticate_request failed")
+                    logger.warn("authenticate_request failed: missing authentication")
                     raise
-            except Exception:
-                logger.warn("authenticate_request failed")
+            except Exception as e:
+                logger.warn("authenticate_request failed: %s", e)
                 raise
 
             if origin: