// 加载Google API客户端库
function loadGoogleAuth() {
  gapi.load('auth2', function() {
    gapi.auth2.init({
      client_id: 'YOUR_CLIENT_ID.apps.googleusercontent.com',
      scope: 'profile email'
    });
  });
}

// 登录并获取用户信息
function signIn() {
  const auth2 = gapi.auth2.getAuthInstance();
  auth2.signIn().then(function(googleUser) {
    const profile = googleUser.getBasicProfile();
    console.log('Email: ' + profile.getEmail());
  }).catch(function(error) {
    console.error('Error signing in: ', error);
  });
}

// 前端获取ID token
const id_token = googleUser.getAuthResponse().id_token;

// 后端验证示例(Node.js)
const { OAuth2Client } = require('google-auth-library');
const client = new OAuth2Client(YOUR_CLIENT_ID);

async function verifyToken(idToken) {
  const ticket = await client.verifyIdToken({
    idToken: idToken,
    audience: YOUR_CLIENT_ID,
  });
  const payload = ticket.getPayload();
  const email = payload['email'];
  console.log('Verified email:', email);
  return email;
}