Don't log 401 as errors

Because there is not much we can do about it, so let's not pollute
our alerts channel with this. Logging a warning is enough.
(we also set a response to avoid an uncaught exception being
 thrown afterwards, as this would result in another error being
 logged)

symfony-server/src/EventListener/ExceptionListener.php

@@ -17,7 +17,17 @@ public function __invoke(Exceptionevent $event): void {
 			$response = new Response();
 			$response->setStatusCode(Response::HTTP_NOT_FOUND);
 			$response->setContent("Not found");
+			$event->setResponse($response);        
+		} else if ($exception->getStatusCode() === Response::HTTP_UNAUTHORIZED) {
+			$this->logger->warning("Caught unauthorized access");
+			$response = new Response();
+			$response->setStatusCode(Response::HTTP_UNAUTHORIZED);
+			$response->setContent("Unauthorized");
 			$event->setResponse($response);
+			// TODO 1: according to this, perhaps this code could be replaced by some conf on this firewall:
+			// > No Authentication entry point configured, returning a 401 HTTP response. Configure "entry_point" on the firewall "main" if you want to modify the response.
+
+			// TODO 2: Perhaps we should instead redirect to the login page?
 		} else {
 			$this->logger->error("Caught exception: " . $exception->getMessage() . "(code: " . $exception->getCode() . "). Stack trace: " . $exception->getTraceAsString());
 		}