youtube auth use api v3 to login into google account

auth.php

<?php
if (!file_exists($file = __DIR__ . '/vendor/autoload.php')) {
  throw new \Exception('please run "composer require google/apiclient:~2.0" in "' . __DIR__ .'"');
}

require_once __DIR__ . '/vendor/autoload.php';
session_start();

$OAUTH2_CLIENT_ID = '751887412551-o95lukoq6blmmlkom33mteojlpnrtbim.apps.googleusercontent.com';
$OAUTH2_CLIENT_SECRET = '9vGd0fvJ3m0_4ePtN4Ms8jNM';


$client = new Google_Client();
$client->setClientId($OAUTH2_CLIENT_ID);
$client->setClientSecret($OAUTH2_CLIENT_SECRET);
$client->setScopes('https://www.googleapis.com/auth/youtube');
$redirect = filter_var('http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'],
    FILTER_SANITIZE_URL);
$client->setRedirectUri($redirect);

// Define an object that will be used to make all API requests.
$youtube = new Google_Service_YouTube($client);

// Check if an auth token exists for the required scopes
$tokenSessionKey = 'token-' . $client->prepareScopes();
if (isset($_GET['code'])) {
  if (strval($_SESSION['state']) !== strval($_GET['state'])) {
    die('The session state did not match.');
  }

  $client->authenticate($_GET['code']);
  $_SESSION[$tokenSessionKey] = $client->getAccessToken();
  header('Location: ' . $redirect);
}

if (isset($_SESSION[$tokenSessionKey])) {
  $client->setAccessToken($_SESSION[$tokenSessionKey]);
    
}
if ($client->getAccessToken()) {
    $_SESSION['halo'] = "hi";
    
    
} else {
  $state = mt_rand();
  $client->setState($state);
  $_SESSION['state'] = $state;
  $authUrl = $client->createAuthUrl();
  echo "<a href='".$authUrl."'>login please</a>";
 }

?>