Google Identity Services is migrating to FedCM APIs. Follow the migration guide to review potential changes and avoid negative impacts for user sign-in to your website.

Handle credential responses with JavaScript functions

Handle credential response

You can set a JavaScript function in the data-callback attribute to handle the returned credential response. See the following code snippet:

<div id="g_id_onload"
     data-client_id="YOUR_GOOGLE_CLIENT_ID"
     data-callback="handleCredentialResponse">
</div>
<script>
  function handleCredentialResponse(response) {
     const responsePayload = decodeJwtResponse(response.credential);

     console.log("ID: " + responsePayload.sub);
     console.log('Full Name: ' + responsePayload.name);
     console.log('Given Name: ' + responsePayload.given_name);
     console.log('Family Name: ' + responsePayload.family_name);
     console.log("Image URL: " + responsePayload.picture);
     console.log("Email: " + responsePayload.email);
  }

  function decodeJwtResponse(token) {
    let base64Url = token.split('.')[1];
    let base64 = base64Url.replace(/-/g, '+').replace(/_/g, '/');
    let jsonPayload = decodeURIComponent(atob(base64).split('').map(function(c) {
        return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
    }).join(''));

    return JSON.parse(jsonPayload);
  }
</script>

You can validate and decode the JWT credential by using a JWT-decoding library for your language. You should also verify the Google ID token on your server side.