<?php
// auth.php

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

$client = new Google_Client();
$client->setClientId('YOUR_CLIENT_ID');
$client->setClientSecret('YOUR_CLIENT_SECRET');
$client->setRedirectUri('YOUR_REDIRECT_URI'); // e.g., http://localhost/yourproject/auth.php
$client->addScope(Google_Service_Tasks::TASKS);

if (!isset($_GET['code'])) {
    $auth_url = $client->createAuthUrl();
    header('Location: ' . filter_var($auth_url, FILTER_SANITIZE_URL));
} else {
    $client->authenticate($_GET['code']);
    $_SESSION['access_token'] = $client->getAccessToken();
    header('Location: ' . filter_var($client->getRedirectUri(), FILTER_SANITIZE_URL));
}