Improve errors

bin/main.dart

@@ -34,9 +34,11 @@ void main(List<String> argsRaw) async {
               );
 
               if (authResponse.statusCode != 200) {
-                return Response.internalServerError(
+                return Response(
+                  authResponse.statusCode,
                   body: json.encode({
-                    "error": "An error occurred: ${authResponse.statusCode}.",
+                    "error":
+                        "An error occurred when calling `authUri`: ${authResponse.body}.",
                   }),
                   headers: {HttpHeaders.contentTypeHeader: "application/json"},
                 );