From dd9ccc980780109f6c2229351afaa304120ec2ca Mon Sep 17 00:00:00 2001
From: Nayana Parameswarappa
 <138813846+Nayana-Parameswarappa@users.noreply.github.com>
Date: Mon, 2 Mar 2026 13:37:44 -0800
Subject: [PATCH] Adding MCPOAuthProvider implementing the MCPSDK
 OAuthClientProvider (#20121)

---
 .../core/src/mcp/mcp-oauth-provider.test.ts   | 84 ++++++++++++++++
 packages/core/src/mcp/mcp-oauth-provider.ts   | 97 +++++++++++++++++++
 2 files changed, 181 insertions(+)
 create mode 100644 packages/core/src/mcp/mcp-oauth-provider.test.ts
 create mode 100644 packages/core/src/mcp/mcp-oauth-provider.ts

diff --git a/packages/core/src/mcp/mcp-oauth-provider.test.ts b/packages/core/src/mcp/mcp-oauth-provider.test.ts
new file mode 100644
index 0000000000..a7891f035b
--- /dev/null
+++ b/packages/core/src/mcp/mcp-oauth-provider.test.ts
@@ -0,0 +1,84 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi } from 'vitest';
+import {
+  MCPOAuthClientProvider,
+  type OAuthAuthorizationResponse,
+} from './mcp-oauth-provider.js';
+import type {
+  OAuthClientInformation,
+  OAuthClientMetadata,
+  OAuthTokens,
+} from '@modelcontextprotocol/sdk/shared/auth.js';
+
+describe('MCPOAuthClientProvider', () => {
+  const mockRedirectUrl = 'http://localhost:8090/callback';
+  const mockClientMetadata: OAuthClientMetadata = {
+    client_name: 'Test Client',
+    redirect_uris: [mockRedirectUrl],
+    grant_types: ['authorization_code', 'refresh_token'],
+    response_types: ['code'],
+    token_endpoint_auth_method: 'client_secret_post',
+    scope: 'test-scope',
+  };
+  const mockState = 'test-state-123';
+
+  describe('oauth flow', () => {
+    it('should support full OAuth flow', async () => {
+      const onRedirectMock = vi.fn();
+      const provider = new MCPOAuthClientProvider(
+        mockRedirectUrl,
+        mockClientMetadata,
+        mockState,
+        onRedirectMock,
+      );
+
+      // Step 1: Save client information
+      const clientInfo: OAuthClientInformation = {
+        client_id: 'my-client-id',
+        client_secret: 'my-client-secret',
+      };
+      provider.saveClientInformation(clientInfo);
+
+      // Step 2: Save code verifier
+      provider.saveCodeVerifier('my-code-verifier');
+
+      // Step 3: Set up callback server
+      const mockAuthResponse: OAuthAuthorizationResponse = {
+        code: 'authorization-code',
+        state: mockState,
+      };
+      const mockServer = {
+        port: Promise.resolve(8090),
+        waitForResponse: vi.fn().mockResolvedValue(mockAuthResponse),
+        close: vi.fn().mockResolvedValue(undefined),
+      };
+      provider.saveCallbackServer(mockServer);
+
+      // Step 4: Redirect to authorization
+      const authUrl = new URL('http://auth.example.com/authorize');
+      await provider.redirectToAuthorization(authUrl);
+
+      // Step 5: Save tokens after exchange
+      const tokens: OAuthTokens = {
+        access_token: 'final-access-token',
+        token_type: 'Bearer',
+        expires_in: 3600,
+        refresh_token: 'final-refresh-token',
+      };
+      provider.saveTokens(tokens);
+
+      // Verify all data is stored correctly
+      expect(provider.clientInformation()).toEqual(clientInfo);
+      expect(provider.codeVerifier()).toBe('my-code-verifier');
+      expect(provider.state()).toBe(mockState);
+      expect(provider.tokens()).toEqual(tokens);
+      expect(onRedirectMock).toHaveBeenCalledWith(authUrl);
+      expect(provider.getSavedCallbackServer()).toBe(mockServer);
+    });
+  });
+});
diff --git a/packages/core/src/mcp/mcp-oauth-provider.ts b/packages/core/src/mcp/mcp-oauth-provider.ts
new file mode 100644
index 0000000000..daf977438c
--- /dev/null
+++ b/packages/core/src/mcp/mcp-oauth-provider.ts
@@ -0,0 +1,97 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { OAuthClientProvider } from '@modelcontextprotocol/sdk/client/auth.js';
+import type {
+  OAuthClientInformation,
+  OAuthClientMetadata,
+  OAuthTokens,
+} from '@modelcontextprotocol/sdk/shared/auth.js';
+import { debugLogger } from '../utils/debugLogger.js';
+
+/**
+ * OAuth authorization response.
+ */
+export interface OAuthAuthorizationResponse {
+  code: string;
+  state: string;
+}
+
+type CallbackServer = {
+  port: Promise<number>;
+  waitForResponse: () => Promise<OAuthAuthorizationResponse>;
+  close: () => Promise<void>;
+};
+
+export class MCPOAuthClientProvider implements OAuthClientProvider {
+  private _clientInformation?: OAuthClientInformation;
+  private _tokens?: OAuthTokens;
+  private _codeVerifier?: string;
+  private _cbServer?: CallbackServer;
+
+  constructor(
+    private readonly _redirectUrl: string | URL,
+    private readonly _clientMetadata: OAuthClientMetadata,
+    private readonly _state?: string | undefined,
+    private readonly _onRedirect: (url: URL) => void = (url) => {
+      debugLogger.log(`Redirect to: ${url.toString()}`);
+    },
+  ) {}
+
+  get redirectUrl(): string | URL {
+    return this._redirectUrl;
+  }
+
+  get clientMetadata(): OAuthClientMetadata {
+    return this._clientMetadata;
+  }
+
+  saveCallbackServer(server: CallbackServer): void {
+    this._cbServer = server;
+  }
+
+  getSavedCallbackServer(): CallbackServer | undefined {
+    return this._cbServer;
+  }
+
+  clientInformation(): OAuthClientInformation | undefined {
+    return this._clientInformation;
+  }
+
+  saveClientInformation(clientInformation: OAuthClientInformation): void {
+    this._clientInformation = clientInformation;
+  }
+
+  tokens(): OAuthTokens | undefined {
+    return this._tokens;
+  }
+
+  saveTokens(tokens: OAuthTokens): void {
+    this._tokens = tokens;
+  }
+
+  async redirectToAuthorization(authorizationUrl: URL): Promise<void> {
+    this._onRedirect(authorizationUrl);
+  }
+
+  saveCodeVerifier(codeVerifier: string): void {
+    this._codeVerifier = codeVerifier;
+  }
+
+  codeVerifier(): string {
+    if (!this._codeVerifier) {
+      throw new Error('No code verifier saved');
+    }
+    return this._codeVerifier;
+  }
+
+  state(): string {
+    if (!this._state) {
+      throw new Error('No code state saved');
+    }
+    return this._state;
+  }
+}