How do I add Google sign-in to my app?

To add Google sign-in, the exact steps depend on your app type, but the overall flow is:

1. Create a Google Cloud project
2. Configure OAuth consent screen
3. Create OAuth client credentials
4. Add Google Sign-In to your app
5. Verify the ID token / handle the callback on your backend
6. Create your own app session

1) Create a Google Cloud project

• Go to the Google Cloud Console
• Create a new project or choose an existing one

2) Configure the OAuth consent screen

• In APIs & Services → OAuth consent screen
• Set:
  • App name
  • Support email
  • Authorized domains
  • Privacy policy / terms URLs if needed
• Add test users if the app is in testing

3) Create OAuth client credentials

In APIs & Services → Credentials:

• Create an OAuth client ID
• Choose the app type:
  • Web application
  • Android
  • iOS
  • Desktop
• For web apps, add:
  • Authorized JavaScript origins
  • Authorized redirect URIs

You’ll get a Client ID and sometimes a Client Secret.

4) Implement the sign-in flow

For web apps

Common approach:

• User clicks “Sign in with Google”
• Google returns an authorization code or ID token
• Your backend verifies it
• Your app creates a session for the user

Google’s newer recommended approach for many web apps is Google Identity Services.

Example front-end button:

<script src="https://accounts.google.com/gsi/client" async defer></script>

<div id="g_id_onload"
     data-client_id="YOUR_CLIENT_ID"
     data-callback="handleCredentialResponse">
</div>
<div class="g_id_signin" data-type="standard"></div>

<script>
  function handleCredentialResponse(response) {
    // response.credential is a JWT ID token
    fetch('/auth/google', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ credential: response.credential })
    });
  }
</script>

Backend verification example

On the server, verify the token using Google libraries.

Node.js example:

import { OAuth2Client } from 'google-auth-library';

const client = new OAuth2Client('YOUR_CLIENT_ID');

app.post('/auth/google', async (req, res) => {
  const { credential } = req.body;

  const ticket = await client.verifyIdToken({
    idToken: credential,
    audience: 'YOUR_CLIENT_ID',
  });

  const payload = ticket.getPayload();
  const googleUserId = payload.sub;
  const email = payload.email;

  // Find/create user in your DB, then create your session
  res.json({ success: true });
});

5) Mobile apps

If you’re building:

• Android: use Google Sign-In / Google Identity Services with Android credentials
• iOS: use Google Sign-In SDK
• Often you’ll send the Google ID token to your backend for verification

6) Security best practices

• Verify the token on the server
• Use HTTPS
• Don’t trust user info from the client alone
• Store your own app session, not the Google token, for auth
• Request only the scopes you need

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If you tell me your stack — for example React, Next.js, Flutter, Android, iOS, Node, Django, etc. — I can give you exact step-by-step instructions and code.