refactor(core): extract shared OAuth flow primitives from MCPOAuthProvider (#20895)

packages/core/src/mcp/oauth-provider.ts

@@ -4,9 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import * as http from 'node:http';
 import * as crypto from 'node:crypto';
-import type * as net from 'node:net';
 import { URL } from 'node:url';
 import { openBrowserSecurely } from '../utils/secure-browser-launcher.js';
 import type { OAuthToken } from './token-storage/types.js';
@@ -16,6 +14,23 @@ import { OAuthUtils, ResourceMismatchError } from './oauth-utils.js';
 import { coreEvents } from '../utils/events.js';
 import { debugLogger } from '../utils/debugLogger.js';
 import { getConsentForOauth } from '../utils/authConsent.js';
+import {
+  generatePKCEParams,
+  startCallbackServer,
+  getPortFromUrl,
+  buildAuthorizationUrl,
+  exchangeCodeForToken,
+  refreshAccessToken as refreshAccessTokenShared,
+  REDIRECT_PATH,
+  type OAuthFlowConfig,
+  type OAuthTokenResponse,
+} from '../utils/oauth-flow.js';
+
+// Re-export types that were moved to oauth-flow.ts for backward compatibility.
+export type {
+  OAuthAuthorizationResponse,
+  OAuthTokenResponse,
+} from '../utils/oauth-flow.js';
 
 /**
  * OAuth configuration for an MCP server.
@@ -34,25 +49,6 @@ export interface MCPOAuthConfig {
   registrationUrl?: string;
 }
 
-/**
- * OAuth authorization response.
- */
-export interface OAuthAuthorizationResponse {
-  code: string;
-  state: string;
-}
-
-/**
- * OAuth token response from the authorization server.
- */
-export interface OAuthTokenResponse {
-  access_token: string;
-  token_type: string;
-  expires_in?: number;
-  refresh_token?: string;
-  scope?: string;
-}
-
 /**
  * Dynamic client registration request (RFC 7591).
  */
@@ -80,18 +76,6 @@ export interface OAuthClientRegistrationResponse {
   scope?: string;
 }
 
-/**
- * PKCE (Proof Key for Code Exchange) parameters.
- */
-interface PKCEParams {
-  codeVerifier: string;
-  codeChallenge: string;
-  state: string;
-}
-
-const REDIRECT_PATH = '/oauth/callback';
-const HTTP_OK = 200;
-
 /**
  * Provider for handling OAuth authentication for MCP servers.
  */
@@ -239,375 +223,18 @@ export class MCPOAuthProvider {
   }
 
   /**
-   * Generate PKCE parameters for OAuth flow.
-   *
-   * @returns PKCE parameters including code verifier, challenge, and state
+   * Build the OAuth resource parameter from an MCP server URL, if available.
+   * Returns undefined if the URL is not provided or cannot be processed.
    */
-  private generatePKCEParams(): PKCEParams {
-    // Generate code verifier (43-128 characters)
-    // using 64 bytes results in ~86 characters, safely above the minimum of 43
-    const codeVerifier = crypto.randomBytes(64).toString('base64url');
-
-    // Generate code challenge using SHA256
-    const codeChallenge = crypto
-      .createHash('sha256')
-      .update(codeVerifier)
-      .digest('base64url');
-
-    // Generate state for CSRF protection
-    const state = crypto.randomBytes(16).toString('base64url');
-
-    return { codeVerifier, codeChallenge, state };
-  }
-
-  /**
-   * Start a local HTTP server to handle OAuth callback.
-   * The server will listen on the specified port (or port 0 for OS assignment).
-   *
-   * @param expectedState The state parameter to validate
-   * @returns Object containing the port (available immediately) and a promise for the auth response
-   */
-  private startCallbackServer(
-    expectedState: string,
-    port?: number,
-  ): {
-    port: Promise<number>;
-    response: Promise<OAuthAuthorizationResponse>;
-  } {
-    let portResolve: (port: number) => void;
-    let portReject: (error: Error) => void;
-    const portPromise = new Promise<number>((resolve, reject) => {
-      portResolve = resolve;
-      portReject = reject;
-    });
-
-    const responsePromise = new Promise<OAuthAuthorizationResponse>(
-      (resolve, reject) => {
-        let serverPort: number;
-
-        const server = http.createServer(
-          async (req: http.IncomingMessage, res: http.ServerResponse) => {
-            try {
-              const url = new URL(req.url!, `http://localhost:${serverPort}`);
-
-              if (url.pathname !== REDIRECT_PATH) {
-                res.writeHead(404);
-                res.end('Not found');
-                return;
-              }
-
-              const code = url.searchParams.get('code');
-              const state = url.searchParams.get('state');
-              const error = url.searchParams.get('error');
-
-              if (error) {
-                res.writeHead(HTTP_OK, { 'Content-Type': 'text/html' });
-                res.end(`
-              <html>
-                <body>
-                  <h1>Authentication Failed</h1>
-                  <p>Error: ${error.replace(/</g, '&lt;').replace(/>/g, '&gt;')}</p>
-                  <p>${(url.searchParams.get('error_description') || '').replace(/</g, '&lt;').replace(/>/g, '&gt;')}</p>
-                  <p>You can close this window.</p>
-                </body>
-              </html>
-            `);
-                server.close();
-                reject(new Error(`OAuth error: ${error}`));
-                return;
-              }
-
-              if (!code || !state) {
-                res.writeHead(400);
-                res.end('Missing code or state parameter');
-                return;
-              }
-
-              if (state !== expectedState) {
-                res.writeHead(400);
-                res.end('Invalid state parameter');
-                server.close();
-                reject(new Error('State mismatch - possible CSRF attack'));
-                return;
-              }
-
-              // Send success response to browser
-              res.writeHead(HTTP_OK, { 'Content-Type': 'text/html' });
-              res.end(`
-            <html>
-              <body>
-                <h1>Authentication Successful!</h1>
-                <p>You can close this window and return to Gemini CLI.</p>
-                <script>window.close();</script>
-              </body>
-            </html>
-          `);
-
-              server.close();
-              resolve({ code, state });
-            } catch (error) {
-              server.close();
-              reject(error);
-            }
-          },
-        );
-
-        server.on('error', (error) => {
-          portReject(error);
-          reject(error);
-        });
-
-        // Determine which port to use (env var, argument, or OS-assigned)
-        let listenPort = 0; // Default to OS-assigned port
-
-        const portStr = process.env['OAUTH_CALLBACK_PORT'];
-        if (portStr) {
-          const envPort = parseInt(portStr, 10);
-          if (isNaN(envPort) || envPort <= 0 || envPort > 65535) {
-            const error = new Error(
-              `Invalid value for OAUTH_CALLBACK_PORT: "${portStr}"`,
-            );
-            portReject(error);
-            reject(error);
-            return;
-          }
-          listenPort = envPort;
-        } else if (port !== undefined) {
-          listenPort = port;
-        }
-
-        server.listen(listenPort, () => {
-          // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-          const address = server.address() as net.AddressInfo;
-          serverPort = address.port;
-          debugLogger.log(
-            `OAuth callback server listening on port ${serverPort}`,
-          );
-          portResolve(serverPort); // Resolve port promise immediately
-        });
-
-        // Timeout after 5 minutes
-        setTimeout(
-          () => {
-            server.close();
-            reject(new Error('OAuth callback timeout'));
-          },
-          5 * 60 * 1000,
-        );
-      },
-    );
-
-    return { port: portPromise, response: responsePromise };
-  }
-
-  /**
-   * Extract the port number from a URL string if available and valid.
-   *
-   * @param urlString The URL string to parse
-   * @returns The port number or undefined if not found or invalid
-   */
-  private getPortFromUrl(urlString?: string): number | undefined {
-    if (!urlString) {
-      return undefined;
-    }
-
+  private buildResourceParam(mcpServerUrl?: string): string | undefined {
+    if (!mcpServerUrl) return undefined;
     try {
-      const url = new URL(urlString);
-      if (url.port) {
-        const parsedPort = parseInt(url.port, 10);
-        if (!isNaN(parsedPort) && parsedPort > 0 && parsedPort <= 65535) {
-          return parsedPort;
-        }
-      }
-    } catch {
-      // Ignore invalid URL
-    }
-
-    return undefined;
-  }
-
-  /**
-   * Build the authorization URL for the OAuth flow.
-
-   *
-   * @param config OAuth configuration
-   * @param pkceParams PKCE parameters
-   * @param redirectPort The port to use for the redirect URI
-   * @param mcpServerUrl The MCP server URL to use as the resource parameter
-   * @returns The authorization URL
-   */
-  private buildAuthorizationUrl(
-    config: MCPOAuthConfig,
-    pkceParams: PKCEParams,
-    redirectPort: number,
-    mcpServerUrl?: string,
-  ): string {
-    const redirectUri =
-      config.redirectUri || `http://localhost:${redirectPort}${REDIRECT_PATH}`;
-
-    const params = new URLSearchParams({
-      client_id: config.clientId!,
-      response_type: 'code',
-      redirect_uri: redirectUri,
-      state: pkceParams.state,
-      code_challenge: pkceParams.codeChallenge,
-      code_challenge_method: 'S256',
-    });
-
-    if (config.scopes && config.scopes.length > 0) {
-      params.append('scope', config.scopes.join(' '));
-    }
-
-    if (config.audiences && config.audiences.length > 0) {
-      params.append('audience', config.audiences.join(' '));
-    }
-
-    // Add resource parameter for MCP OAuth spec compliance
-    // Only add if we have an MCP server URL (indicates MCP OAuth flow, not standard OAuth)
-    if (mcpServerUrl) {
-      try {
-        params.append(
-          'resource',
-          OAuthUtils.buildResourceParameter(mcpServerUrl),
-        );
-      } catch (error) {
-        debugLogger.warn(
-          `Could not add resource parameter: ${getErrorMessage(error)}`,
-        );
-      }
-    }
-
-    const url = new URL(config.authorizationUrl!);
-    params.forEach((value, key) => {
-      url.searchParams.append(key, value);
-    });
-    return url.toString();
-  }
-
-  /**
-   * Exchange authorization code for tokens.
-   *
-   * @param config OAuth configuration
-   * @param code Authorization code
-   * @param codeVerifier PKCE code verifier
-   * @param redirectPort The port to use for the redirect URI
-   * @param mcpServerUrl The MCP server URL to use as the resource parameter
-   * @returns The token response
-   */
-  private async exchangeCodeForToken(
-    config: MCPOAuthConfig,
-    code: string,
-    codeVerifier: string,
-    redirectPort: number,
-    mcpServerUrl?: string,
-  ): Promise<OAuthTokenResponse> {
-    const redirectUri =
-      config.redirectUri || `http://localhost:${redirectPort}${REDIRECT_PATH}`;
-
-    const params = new URLSearchParams({
-      grant_type: 'authorization_code',
-      code,
-      redirect_uri: redirectUri,
-      code_verifier: codeVerifier,
-      client_id: config.clientId!,
-    });
-
-    if (config.clientSecret) {
-      params.append('client_secret', config.clientSecret);
-    }
-
-    if (config.audiences && config.audiences.length > 0) {
-      params.append('audience', config.audiences.join(' '));
-    }
-
-    // Add resource parameter for MCP OAuth spec compliance
-    // Only add if we have an MCP server URL (indicates MCP OAuth flow, not standard OAuth)
-    if (mcpServerUrl) {
-      const resourceUrl = mcpServerUrl;
-      try {
-        params.append(
-          'resource',
-          OAuthUtils.buildResourceParameter(resourceUrl),
-        );
-      } catch (error) {
-        debugLogger.warn(
-          `Could not add resource parameter: ${getErrorMessage(error)}`,
-        );
-      }
-    }
-
-    const response = await fetch(config.tokenUrl!, {
-      method: 'POST',
-      headers: {
-        'Content-Type': 'application/x-www-form-urlencoded',
-        Accept: 'application/json, application/x-www-form-urlencoded',
-      },
-      body: params.toString(),
-    });
-
-    const responseText = await response.text();
-    const contentType = response.headers.get('content-type') || '';
-
-    if (!response.ok) {
-      // Try to parse error from form-urlencoded response
-      let errorMessage: string | null = null;
-      try {
-        const errorParams = new URLSearchParams(responseText);
-        const error = errorParams.get('error');
-        const errorDescription = errorParams.get('error_description');
-        if (error) {
-          errorMessage = `Token exchange failed: ${error} - ${errorDescription || 'No description'}`;
-        }
-      } catch {
-        // Fall back to raw error
-      }
-      throw new Error(
-        errorMessage ||
-          `Token exchange failed: ${response.status} - ${responseText}`,
-      );
-    }
-
-    // Log unexpected content types for debugging
-    if (
-      !contentType.includes('application/json') &&
-      !contentType.includes('application/x-www-form-urlencoded')
-    ) {
+      return OAuthUtils.buildResourceParameter(mcpServerUrl);
+    } catch (error) {
       debugLogger.warn(
-        `Token endpoint returned unexpected content-type: ${contentType}. ` +
-          `Expected application/json or application/x-www-form-urlencoded. ` +
-          `Will attempt to parse response.`,
+        `Could not add resource parameter: ${getErrorMessage(error)}`,
       );
-    }
-
-    // Try to parse as JSON first, fall back to form-urlencoded
-    try {
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-      return JSON.parse(responseText) as OAuthTokenResponse;
-    } catch {
-      // Parse form-urlencoded response
-      const tokenParams = new URLSearchParams(responseText);
-      const accessToken = tokenParams.get('access_token');
-      const tokenType = tokenParams.get('token_type') || 'Bearer';
-      const expiresIn = tokenParams.get('expires_in');
-      const refreshToken = tokenParams.get('refresh_token');
-      const scope = tokenParams.get('scope');
-
-      if (!accessToken) {
-        // Check for error in response
-        const error = tokenParams.get('error');
-        const errorDescription = tokenParams.get('error_description');
-        throw new Error(
-          `Token exchange failed: ${error || 'no_access_token'} - ${errorDescription || responseText}`,
-        );
-      }
-
-      return {
-        access_token: accessToken,
-        token_type: tokenType,
-        expires_in: expiresIn ? parseInt(expiresIn, 10) : undefined,
-        refresh_token: refreshToken || undefined,
-        scope: scope || undefined,
-      } as OAuthTokenResponse;
+      return undefined;
     }
   }
 
@@ -626,112 +253,21 @@ export class MCPOAuthProvider {
     tokenUrl: string,
     mcpServerUrl?: string,
   ): Promise<OAuthTokenResponse> {
-    const params = new URLSearchParams({
-      grant_type: 'refresh_token',
-      refresh_token: refreshToken,
-      client_id: config.clientId!,
-    });
-
-    if (config.clientSecret) {
-      params.append('client_secret', config.clientSecret);
+    if (!config.clientId) {
+      throw new Error('Missing required clientId for token refresh');
     }
 
-    if (config.scopes && config.scopes.length > 0) {
-      params.append('scope', config.scopes.join(' '));
-    }
-
-    if (config.audiences && config.audiences.length > 0) {
-      params.append('audience', config.audiences.join(' '));
-    }
-
-    // Add resource parameter for MCP OAuth spec compliance
-    // Only add if we have an MCP server URL (indicates MCP OAuth flow, not standard OAuth)
-    if (mcpServerUrl) {
-      try {
-        params.append(
-          'resource',
-          OAuthUtils.buildResourceParameter(mcpServerUrl),
-        );
-      } catch (error) {
-        debugLogger.warn(
-          `Could not add resource parameter: ${getErrorMessage(error)}`,
-        );
-      }
-    }
-
-    const response = await fetch(tokenUrl, {
-      method: 'POST',
-      headers: {
-        'Content-Type': 'application/x-www-form-urlencoded',
-        Accept: 'application/json, application/x-www-form-urlencoded',
+    return refreshAccessTokenShared(
+      {
+        clientId: config.clientId,
+        clientSecret: config.clientSecret,
+        scopes: config.scopes,
+        audiences: config.audiences,
       },
-      body: params.toString(),
-    });
-
-    const responseText = await response.text();
-    const contentType = response.headers.get('content-type') || '';
-
-    if (!response.ok) {
-      // Try to parse error from form-urlencoded response
-      let errorMessage: string | null = null;
-      try {
-        const errorParams = new URLSearchParams(responseText);
-        const error = errorParams.get('error');
-        const errorDescription = errorParams.get('error_description');
-        if (error) {
-          errorMessage = `Token refresh failed: ${error} - ${errorDescription || 'No description'}`;
-        }
-      } catch {
-        // Fall back to raw error
-      }
-      throw new Error(
-        errorMessage ||
-          `Token refresh failed: ${response.status} - ${responseText}`,
-      );
-    }
-
-    // Log unexpected content types for debugging
-    if (
-      !contentType.includes('application/json') &&
-      !contentType.includes('application/x-www-form-urlencoded')
-    ) {
-      debugLogger.warn(
-        `Token refresh endpoint returned unexpected content-type: ${contentType}. ` +
-          `Expected application/json or application/x-www-form-urlencoded. ` +
-          `Will attempt to parse response.`,
-      );
-    }
-
-    // Try to parse as JSON first, fall back to form-urlencoded
-    try {
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
-      return JSON.parse(responseText) as OAuthTokenResponse;
-    } catch {
-      // Parse form-urlencoded response
-      const tokenParams = new URLSearchParams(responseText);
-      const accessToken = tokenParams.get('access_token');
-      const tokenType = tokenParams.get('token_type') || 'Bearer';
-      const expiresIn = tokenParams.get('expires_in');
-      const refreshToken = tokenParams.get('refresh_token');
-      const scope = tokenParams.get('scope');
-
-      if (!accessToken) {
-        // Check for error in response
-        const error = tokenParams.get('error');
-        const errorDescription = tokenParams.get('error_description');
-        throw new Error(
-          `Token refresh failed: ${error || 'unknown_error'} - ${errorDescription || responseText}`,
-        );
-      }
-
-      return {
-        access_token: accessToken,
-        token_type: tokenType,
-        expires_in: expiresIn ? parseInt(expiresIn, 10) : undefined,
-        refresh_token: refreshToken || undefined,
-        scope: scope || undefined,
-      } as OAuthTokenResponse;
-    }
+      refreshToken,
+      tokenUrl,
+      this.buildResourceParam(mcpServerUrl),
+    );
   }
 
   /**
@@ -830,17 +366,14 @@ export class MCPOAuthProvider {
     }
 
     // Generate PKCE parameters
-    const pkceParams = this.generatePKCEParams();
+    const pkceParams = generatePKCEParams();
 
     // Determine preferred port from redirectUri if available
-    const preferredPort = this.getPortFromUrl(config.redirectUri);
+    const preferredPort = getPortFromUrl(config.redirectUri);
 
     // Start callback server first to allocate port
     // This ensures we only create one server and eliminates race conditions
-    const callbackServer = this.startCallbackServer(
-      pkceParams.state,
-      preferredPort,
-    );
+    const callbackServer = startCallbackServer(pkceParams.state, preferredPort);
 
     // Wait for server to start and get the allocated port
     // We need this port for client registration and auth URL building
@@ -892,12 +425,24 @@ export class MCPOAuthProvider {
       );
     }
 
+    // Build flow config for shared utilities
+    const flowConfig: OAuthFlowConfig = {
+      clientId: config.clientId,
+      clientSecret: config.clientSecret,
+      authorizationUrl: config.authorizationUrl,
+      tokenUrl: config.tokenUrl,
+      scopes: config.scopes,
+      audiences: config.audiences,
+      redirectUri: config.redirectUri,
+    };
+
     // Build authorization URL
-    const authUrl = this.buildAuthorizationUrl(
-      config,
+    const resource = this.buildResourceParam(mcpServerUrl);
+    const authUrl = buildAuthorizationUrl(
+      flowConfig,
       pkceParams,
       redirectPort,
-      mcpServerUrl,
+      resource,
     );
 
     const userConsent = await getConsentForOauth(
@@ -933,12 +478,12 @@ ${authUrl}
     );
 
     // Exchange code for tokens
-    const tokenResponse = await this.exchangeCodeForToken(
-      config,
+    const tokenResponse = await exchangeCodeForToken(
+      flowConfig,
       code,
       pkceParams.codeVerifier,
       redirectPort,
-      mcpServerUrl,
+      resource,
     );
 
     // Convert to our token format