feat(toolbox-core): Add helper methods for retrieving Google ID Tokens (#41)

* feat: add client headers

* lint

* lint

* resolve comments

* disable any lint warning on a line

* working code

* fix tests

* lint

* Only intercept request if it is sent to the toolbox server

* move changes to correct pr

Author: twishabansal

packages/toolbox-core/package-lock.json

@@ -15,8 +15,16 @@
         "agents",
         "mcp"
     ],
-    "main": "build/client.js",
-    "types": "build/client.d.ts",
+    "exports": {
+        ".": {
+            "import": "./build/client.js",
+            "types": "./build/client.d.ts"
+        },
+        "./auth": {
+            "import": "./build/authMethods.js",
+            "types": "./build/authMethods.d.ts"
+        }
+    },
     "repository": {
         "type": "git",
         "url": "git+https://github.com/googleapis/mcp-toolbox-sdk-js.git"
@@ -45,7 +53,6 @@
         "@types/tmp": "^0.2.6",
         "cross-env": "^7.0.3",
         "fs-extra": "^11.3.0",
-        "google-auth-library": "^9.15.1",
         "gts": "^5.3.1",
         "jest": "^29.7.0",
         "tmp": "^0.2.3",
@@ -54,6 +61,7 @@
     },
     "dependencies": {
         "axios": "^1.9.0",
+        "google-auth-library": "^9.15.1",
         "zod": "^3.24.4"
     }
 }

packages/toolbox-core/package.json

@@ -0,0 +1,10 @@
+import {GoogleAuth} from 'google-auth-library';
+
+async function getGoogleIdToken(url: string) {
+  const auth = new GoogleAuth();
+  const client = await auth.getIdTokenClient(url);
+  const id_token = await client.idTokenProvider.fetchIdToken(url);
+  return `Bearer ${id_token}`;
+}
+
+export {getGoogleIdToken};

packages/toolbox-core/src/toolbox_core/authMethods.ts

@@ -0,0 +1,64 @@
+// Copyright 2025 Google LLC
+//
+// 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 {getGoogleIdToken} from '../src/toolbox_core/authMethods';
+import {GoogleAuth} from 'google-auth-library';
+
+jest.mock('google-auth-library', () => ({GoogleAuth: jest.fn()}));
+
+describe('getGoogleIdToken', () => {
+  const mockUrl = 'https://example.com';
+  const mockToken = 'mock-id-token';
+
+  let mockGetIdTokenClient: jest.Mock;
+  let mockFetchIdToken: jest.Mock;
+
+  beforeEach(() => {
+    // Reset mocks before each test
+    mockFetchIdToken = jest.fn().mockResolvedValue(mockToken);
+    mockGetIdTokenClient = jest.fn().mockResolvedValue({
+      idTokenProvider: {
+        fetchIdToken: mockFetchIdToken,
+      },
+    });
+    (GoogleAuth as jest.MockedClass<typeof GoogleAuth>).mockImplementation(
+      () =>
+        ({
+          getIdTokenClient: mockGetIdTokenClient,
+        }) as unknown as GoogleAuth
+    );
+  });
+
+  it('should return a Bearer token on successful fetch', async () => {
+    const token = await getGoogleIdToken(mockUrl);
+    expect(token).toBe(`Bearer ${mockToken}`);
+    expect(GoogleAuth).toHaveBeenCalledTimes(1);
+    expect(mockGetIdTokenClient).toHaveBeenCalledWith(mockUrl);
+    expect(mockFetchIdToken).toHaveBeenCalledWith(mockUrl);
+  });
+
+  it('should propagate errors from getIdTokenClient', async () => {
+    const errorMessage = 'Failed to get ID token client';
+    mockGetIdTokenClient.mockRejectedValue(new Error(errorMessage));
+
+    await expect(getGoogleIdToken(mockUrl)).rejects.toThrow(errorMessage);
+  });
+
+  it('should propagate errors from fetchIdToken', async () => {
+    const errorMessage = 'Failed to fetch ID token';
+    mockFetchIdToken.mockRejectedValue(new Error(errorMessage));
+
+    await expect(getGoogleIdToken(mockUrl)).rejects.toThrow(errorMessage);
+  });
+});