Allow running the authentication service on a different base path

frontend/src/config.ts

@@ -0,0 +1,27 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// 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.
+
+export type AppConfig = {
+  root: string;
+  graphqlEndpoint: string;
+};
+
+interface IWindow {
+  APP_CONFIG?: AppConfig;
+}
+
+const config: AppConfig = (typeof window !== "undefined" &&
+  (window as IWindow).APP_CONFIG) || { root: "/", graphqlEndpoint: "/graphql" };
+
+export default config;