STB_2018_Warmup.php

<?php

if (empty($_POST['hmac']) || empty($_POST['host'])) {
    header('HTTP/1.0 400 Bad Request');
    exit;
}

$secret = getenv("SECRET"); 

if (isset($_POST['nonce']))
	$secret = hash_hmac('sha256', $_POST['nonce'], $secret);

$hmac = hash_hmac('sha256', $_POST['host'], $secret);

if ($hmac !== $_POST['hmac']) {
    header('HTTP/1.0 403 Forbidden');
    exit;
}

echo exec("host ".$_POST['host']);
?>