feat(vertex): add AuthClient interface support for improved auth flexibility

- Add authClient option to ClientOptions interface
- Support both authClient and googleAuth for backward compatibility
- Update documentation with examples for different auth methods
- Add support for Impersonated credentials via AuthClient interface

Addresses CE-673

Author: dtmeadows

packages/vertex-sdk/README.md

@@ -41,6 +41,66 @@ main();
 
 For more details on how to use the SDK, see the [README.md for the main Anthropic SDK](https://github.com/anthropics/anthropic-sdk-typescript/tree/main#anthropic-typescript-api-library) which this library extends.
 
+## Authentication
+
+This library supports multiple authentication methods:
+
+### Default authentication
+
+The client automatically uses the default Google Cloud authentication flow:
+
+```js
+import { AnthropicVertex } from '@anthropic-ai/vertex-sdk';
+
+// Uses default authentication and environment variables
+const client = new AnthropicVertex({
+  region: 'us-central1',
+  projectId: 'my-project-id',
+});
+```
+
+### Custom GoogleAuth configuration
+
+You can customize the authentication using the `googleAuth` option:
+
+```js
+import { AnthropicVertex } from '@anthropic-ai/vertex-sdk';
+import { GoogleAuth } from 'google-auth-library';
+
+const client = new AnthropicVertex({
+  googleAuth: new GoogleAuth({
+    scopes: 'https://www.googleapis.com/auth/cloud-platform',
+    keyFile: '/path/to/service-account.json',
+  }),
+  region: 'us-central1',
+  projectId: 'my-project-id',
+});
+```
+
+### Pre-configured AuthClient
+
+For advanced use cases like impersonation, you can provide a pre-configured `AuthClient`:
+
+```js
+import { AnthropicVertex } from '@anthropic-ai/vertex-sdk';
+import { GoogleAuth, Impersonated } from 'google-auth-library';
+
+// Create an impersonated credential
+const authClient = new Impersonated({
+  sourceClient: await new GoogleAuth().getClient(),
+  targetPrincipal: '[email protected]',
+  lifetime: 30,
+  delegates: [],
+  targetScopes: ['https://www.googleapis.com/auth/cloud-platform'],
+});
+
+const client = new AnthropicVertex({
+  authClient,
+  region: 'us-central1',
+  projectId: 'my-project-id',
+});
+```
+
 ## Requirements
 
 TypeScript >= 4.5 is supported.

packages/vertex-sdk/examples/vertex.ts

@@ -1,11 +1,37 @@
 #!/usr/bin/env -S npm run tsn -T
 
 import { AnthropicVertex } from '@anthropic-ai/vertex-sdk';
+import { GoogleAuth, Impersonated } from 'google-auth-library';
 
+// Example 1: Default configuration
 // Reads from the `CLOUD_ML_REGION` & `ANTHROPIC_VERTEX_PROJECT_ID`
 // environment variables.
 const client = new AnthropicVertex();
 
+// Example 2: Using googleAuth (existing approach)
+const clientWithGoogleAuth = new AnthropicVertex({
+  googleAuth: new GoogleAuth({ scopes: 'https://www.googleapis.com/auth/cloud-platform' }),
+  region: 'us-central1',
+  projectId: 'my-project',
+});
+
+// Example 3: Using authClient (new approach) with Impersonated credentials
+async function createClientWithImpersonation() {
+  const authClient = new Impersonated({
+    sourceClient: await new GoogleAuth().getClient(),
+    targetPrincipal: '[email protected]',
+    lifetime: 30,
+    delegates: [],
+    targetScopes: ['https://www.googleapis.com/auth/cloud-platform'],
+  });
+
+  return new AnthropicVertex({
+    authClient,
+    region: 'us-central1',
+    projectId: 'my-project',
+  });
+}
+
 async function main() {
   const result = await client.messages.create({
     messages: [

packages/vertex-sdk/src/client.ts

@@ -1,6 +1,6 @@
 import { BaseAnthropic, ClientOptions as CoreClientOptions } from '@anthropic-ai/sdk/client';
 import * as Resources from '@anthropic-ai/sdk/resources/index';
-import { GoogleAuth } from 'google-auth-library';
+import { GoogleAuth, AuthClient } from 'google-auth-library';
 import { readEnv } from './internal/utils/env';
 import { FinalRequestOptions } from './internal/request-options';
 import { FinalizedRequestInit } from './internal/types';
@@ -27,22 +27,43 @@ export type ClientOptions = Omit<CoreClientOptions, 'apiKey' | 'authToken'> & {
    * ```
    */
   googleAuth?: GoogleAuth | null | undefined;
+
+  /**
+   * Provide a pre-configured `AuthClient` instance from the
+   * [google-auth-library](https://www.npmjs.com/package/google-auth-library) package.
+   *
+   * This is useful when you want to use a specific authentication method like
+   * Impersonated credentials:
+   * ```ts
+   * new AnthropicVertex({
+   *   authClient: new Impersonated({
+   *     sourceClient: await new GoogleAuth().getClient(),
+   *     targetPrincipal: 'impersonated-account@projectID.iam.gserviceaccount.com',
+   *     lifetime: 30,
+   *     delegates: [],
+   *     targetScopes: ['https://www.googleapis.com/auth/cloud-platform']
+   *   })
+   * })
+   * ```
+   */
+  authClient?: AuthClient | null | undefined;
 };
 
 export class AnthropicVertex extends BaseAnthropic {
   region: string;
   projectId: string | null;
   accessToken: string | null;
 
-  private _auth: GoogleAuth;
-  private _authClientPromise: ReturnType<GoogleAuth['getClient']>;
+  private _auth?: GoogleAuth;
+  private _authClientPromise: Promise<AuthClient>;
 
   /**
    * API Client for interfacing with the Anthropic Vertex API.
    *
    * @param {string | null} opts.accessToken
    * @param {string | null} opts.projectId
    * @param {GoogleAuth} opts.googleAuth - Override the default google auth config
+   * @param {AuthClient} opts.authClient - Provide a pre-configured AuthClient instance (alternative to googleAuth)
    * @param {string | null} [opts.region=process.env['CLOUD_ML_REGION']]
    * @param {string} [opts.baseURL=process.env['ANTHROPIC_VERTEX__BASE_URL'] ?? https://${region}-aiplatform.googleapis.com/v1] - Override the default base URL for the API.
    * @param {number} [opts.timeout=10 minutes] - The maximum amount of time (in milliseconds) the client will wait for a response before timing out.
@@ -74,9 +95,14 @@ export class AnthropicVertex extends BaseAnthropic {
     this.projectId = projectId;
     this.accessToken = opts.accessToken ?? null;
 
-    this._auth =
-      opts.googleAuth ?? new GoogleAuth({ scopes: 'https://www.googleapis.com/auth/cloud-platform' });
-    this._authClientPromise = this._auth.getClient();
+    // Support both authClient and googleAuth for backward compatibility
+    if (opts.authClient) {
+      this._authClientPromise = Promise.resolve(opts.authClient);
+    } else {
+      this._auth =
+        opts.googleAuth ?? new GoogleAuth({ scopes: 'https://www.googleapis.com/auth/cloud-platform' });
+      this._authClientPromise = this._auth.getClient();
+    }
   }
 
   messages: MessagesResource = makeMessagesResource(this);