1. Go to this page and download the library: Download mcrock/allegroapi library. Choose the download type require.
2. Extract the ZIP file and open the index.php.
3. Add this code to the index.php.
<?php
require_once('vendor/autoload.php');
/* Start to develop here. Best regards https://php-download.com/ */
$client = new RestClient($credentials);
$authService = $client->getAuthService();
//now redirect to URL generated from this method:
header('Location: '.$authService->getAuthUrl());