/**
 * Verify the request signature that was received.
 *
 * This is harder to spoof as it uses your secret key.
 *
 * @return bool
 */
function verify_request_signature()
{
    if (empty($_GET['s'])) {
        return false;
    }
    $params = $_GET;
    $signature = $params['s'];
    unset($params['s']);
    $request = new Request($params);
    return $request->signature_equals($signature);
}