Create ServerPermissionClient and add it to example backend

Signed-off-by: Joon Park <joonp@spotify.com>

plugins/permission-node/src/ServerPermissionClient.ts

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * 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.
+ */
+
+import { ServerTokenManager } from '@backstage/backend-common';
+import { Config } from '@backstage/config';
+import {
+  AuthorizeRequest,
+  AuthorizeRequestOptions,
+  AuthorizeResponse,
+  AuthorizeResult,
+  DiscoveryApi,
+  PermissionClient,
+} from '@backstage/plugin-permission-common';
+
+export class ServerPermissionClient extends PermissionClient {
+  private readonly serverTokenManager: ServerTokenManager;
+
+  constructor(options: {
+    discoveryApi: DiscoveryApi;
+    configApi: Config;
+    serverTokenManager: ServerTokenManager;
+  }) {
+    const { discoveryApi, configApi, serverTokenManager } = options;
+    super({ discoveryApi, configApi });
+    this.serverTokenManager = serverTokenManager;
+  }
+
+  async authorize(
+    requests: AuthorizeRequest[],
+    options?: AuthorizeRequestOptions,
+  ): Promise<AuthorizeResponse[]> {
+    if (await this.isValidServerToken(options?.token)) {
+      return requests.map(_ => ({ result: AuthorizeResult.ALLOW }));
+    }
+    return super.authorize(requests, options);
+  }
+
+  private async isValidServerToken(
+    token: string | undefined,
+  ): Promise<boolean> {
+    if (!token) {
+      return false;
+    }
+    return this.serverTokenManager
+      .authenticate(token)
+      .then(() => true)
+      .catch(() => false);
+  }
+}

plugins/permission-node/src/index.ts

@@ -22,3 +22,4 @@
 export * from './integration';
 export * from './policy';
 export * from './types';
+export { ServerPermissionClient } from './ServerPermissionClient';