1 files changed, 119 insertions, 0 deletions
diff --git a/packages/core/src/code_assist/login.ts b/packages/core/src/code_assist/login.ts
new file mode 100644
index 00000000..a94b21d4
--- /dev/null
+++ b/packages/core/src/code_assist/login.ts
@@ -0,0 +1,119 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { OAuth2Client } from 'google-auth-library';
+import * as http from 'http';
+import url from 'url';
+import crypto from 'crypto';
+import * as net from 'net';
+
+//  OAuth Client ID used to initiate OAuth2Client class.
+const OAUTH_CLIENT_ID =
+  '681255809395-oo8ft2oprdrnp9e3aqf6av3hmdib135j.apps.googleusercontent.com';
+
+// OAuth Secret value used to initiate OAuth2Client class.
+const OAUTH_CLIENT_NOT_SO_SECRET = process.env.GCA_OAUTH_SECRET;
+
+// OAuth Scopes for Cloud Code authorization.
+const OAUTH_SCOPE = [
+  'https://www.googleapis.com/auth/cloud-platform',
+  'https://www.googleapis.com/auth/userinfo.email',
+  'https://www.googleapis.com/auth/userinfo.profile',
+];
+
+const HTTP_REDIRECT = 301;
+const SIGN_IN_SUCCESS_URL =
+  'https://developers.google.com/gemini-code-assist/auth_success_gemini';
+const SIGN_IN_FAILURE_URL =
+  'https://developers.google.com/gemini-code-assist/auth_failure_gemini';
+
+export async function doGCALogin(): Promise<OAuth2Client> {
+  const redirectPort: number = await getAvailablePort();
+  const client: OAuth2Client = await createOAuth2Client(redirectPort);
+  await login(client, redirectPort);
+  return client;
+}
+
+function createOAuth2Client(redirectPort: number): OAuth2Client {
+  return new OAuth2Client({
+    clientId: OAUTH_CLIENT_ID,
+    clientSecret: OAUTH_CLIENT_NOT_SO_SECRET,
+    redirectUri: `http://localhost:${redirectPort}/oauth2redirect`,
+  });
+}
+
+/**
+ * Returns first available port in user's machine
+ * @returns port number
+ */
+function getAvailablePort(): Promise<number> {
+  return new Promise((resolve, reject) => {
+    let port = 0;
+    try {
+      const server = net.createServer();
+      server.listen(0, () => {
+        const address = server.address()! as net.AddressInfo;
+        port = address.port;
+      });
+      server.on('listening', () => {
+        server.close();
+        server.unref();
+      });
+      server.on('error', (e) => reject(e));
+      server.on('close', () => resolve(port));
+    } catch (e) {
+      reject(e);
+    }
+  });
+}
+
+function login(oAuth2Client: OAuth2Client, port: number): Promise<boolean> {
+  return new Promise((resolve, reject) => {
+    const state = crypto.randomBytes(32).toString('hex');
+    const authURL: string = oAuth2Client.generateAuthUrl({
+      access_type: 'offline',
+      scope: OAUTH_SCOPE,
+      state,
+    });
+
+    console.log('Login:\n\n', authURL);
+
+    const server = http
+      .createServer(async (req, res) => {
+        try {
+          if (req.url!.indexOf('/oauth2callback') > -1) {
+            // acquire the code from the querystring, and close the web server.
+            const qs = new url.URL(req.url!).searchParams;
+            if (qs.get('error')) {
+              console.error(`Error during authentication: ${qs.get('error')}`);
+
+              res.writeHead(HTTP_REDIRECT, { Location: SIGN_IN_FAILURE_URL });
+              res.end();
+              resolve(false);
+            } else if (qs.get('state') !== state) {
+              //check state value
+              console.log('State mismatch. Possible CSRF attack');
+
+              res.end('State mismatch. Possible CSRF attack');
+              resolve(false);
+            } else if (!qs.get('code')) {
+              const { tokens } = await oAuth2Client.getToken(qs.get('code')!);
+              console.log('Logged in! Tokens:\n\n', tokens);
+
+              oAuth2Client.setCredentials(tokens);
+              res.writeHead(HTTP_REDIRECT, { Location: SIGN_IN_SUCCESS_URL });
+              res.end();
+              resolve(true);
+            }
+          }
+        } catch (e) {
+          reject(e);
+        }
+        server.close();
+      })
+      .listen(port);
+  });
+}