Integrating Google Sign-In into your web app

 Google Sign-In manages the OAuth 2.0 flow and token lifecycle, simplifying your integration with Google APIs. A user always has the option to revoke access to an application at any time.

This document describes how to complete a basic Google Sign-In integration.

Create authorization credentials

Any application that uses OAuth 2.0 to access Google APIs must have authorization credentials that identify the application to Google's OAuth 2.0 server. The following steps explain how to create credentials for your project. Your applications can then use the credentials to access APIs that you have enabled for that project.

1. Go to the Credentials page.
2. Click Create credentials > OAuth client ID.
3. Select the Web application application type.
4. Name your OAuth 2.0 client and click Create

After configuration is complete, take note of the client ID that was created. You will need the client ID to complete the next steps. (A client secret is also created, but you need it only for server-side operations.)

Load the Google Platform Library

You must include the Google Platform Library on your web pages that integrate Google Sign-In.

<script src="https://apis.google.com/js/platform.js" async defer></script>

Specify your app's client ID

Specify the client ID you created for your app in the Google Developers Console with the google-signin-client_id meta element.

<meta name="google-signin-client_id" content="YOUR_CLIENT_ID.apps.googleusercontent.com">

Note: You can also specify your app's client ID with the client_id parameter of the gapi.auth2.init() method.

Add a Google Sign-In button

The easiest way to add a Google Sign-In button to your site is to use an automatically rendered sign-in button. With only a few lines of code, you can add a button that automatically configures itself to have the appropriate text, logo, and colors for the sign-in state of the user and the scopes you request.

To create a Google Sign-In button that uses the default settings, add a div element with the class g-signin2 to your sign-in page:

<div class="g-signin2" data-onsuccess="onSignIn"></div>

The following is an example of the default Google Sign-In button:

Get profile information

After you have signed in a user with Google using the default scopes, you can access the user's Google ID, name, profile URL, and email address.

To retrieve profile information for a user, use the getBasicProfile() method.

function onSignIn(googleUser) {
  var profile = googleUser.getBasicProfile();
  console.log('ID: ' + profile.getId()); // Do not send to your backend! Use an ID token instead.
  console.log('Name: ' + profile.getName());
  console.log('Image URL: ' + profile.getImageUrl());
  console.log('Email: ' + profile.getEmail()); // This is null if the 'email' scope is not present.
}

Important: Do not use the Google IDs returned by getId() or the user's profile information to communicate the currently signed in user to your backend server. Instead, send ID tokens, which can be securely validated on the server.

Sign out a user

You can enable users to sign out of your app without signing out of Google by adding a sign-out button or link to your site. To create a sign-out link, attach a function that calls the GoogleAuth.signOut() method to the link's onclick event.

<a href="#" onclick="signOut();">Sign out</a>
<script>
  function signOut() {
    var auth2 = gapi.auth2.getAuthInstance();
    auth2.signOut().then(function () {
      console.log('User signed out.');
    });
  }
</script>