Google login using PHP and Google Client Library version 2

login.php

<?php
/*
 * Please install Google client library using composer. Use below command
 * composer require google/apiclient:"^2.0"
 */

// Turn ON error reporting
error_reporting(E_ALL);
ini_set('display_errors', 1);

// include autoload.php for including Google client library installed using composer
require('vendor/autoload.php');

// Set below keys
define('GOOGLE_CLIENT_ID', 'enter-google-client-id');
define('GOOGLE_CLIENT_SECRET', 'enter-google-client-secret');
define('GOOGLE_REDIRECT_URL', 'redirect-url-which-is-url-to-current-script');

$client = new Google_Client();
$client->setApplicationName('Sample Google Login by Perials');
$client->setClientId(GOOGLE_CLIENT_ID);
$client->setClientSecret(GOOGLE_CLIENT_SECRET);
$client->setRedirectUri(GOOGLE_REDIRECT_URL);

if (isset($_GET['code'])) {
    $token = $client->fetchAccessTokenWithAuthCode($_GET['code']);
    // store the token in Session
    $_SESSION['access_token'] = $token;
}

// if access_token session is set then user has already logged in
if($_SESSION['access_token']) {
    $attributes = $client->verifyIdToken($_SESSION['access_token']['id_token'], GOOGLE_CLIENT_ID);
    print_r($attributes);
    // Above will print an array which should contain below keys
    // name
    // picture
    // email
}
else {
    $scopes = [ Google_Service_Oauth2::USERINFO_PROFILE, Google_Service_Oauth2::USERINFO_EMAIL ];
    $authUrl = $client->createAuthUrl($scopes);
    ?>
    <a href="<?php echo $authUrl; ?>">Click to login via Google</a>
    <?php
}