Test Firewall - Minimal script to prove to hosters that access to certain domains is not possible

test-firewall.php

<?php

// composer require guzzlehttp/guzzle

require __DIR__ . '/vendor/autoload.php';

use GuzzleHttp\Client;

$client = new Client(['timeout'  => 2]);
$urls = [
    'https://example.com',
    'https://wikipedia.de/',
    'https://api.my-domain.de/',
    'https://stageing.my-domain.de/index.php?id=53&L=0',
    'https://my-domain.de/index.php?id=53&L=0'
];
foreach ($urls as $url) {
    echo PHP_EOL . $url . ' ';
    try {
        $response = $client->request('GET', $url);
    } catch (Exception $e) {
        echo 'Error ' . print_r($e->getMessage(), true);
        continue;
    }
    print_r($response->getStatusCode());
}