protected function appendSecretToWebhook($key, $value)
    {
        if (($webhook = $this->flow->getWebhookSecret())
            && in_array($key, ['urlConfirmation', 'urlCallBack', 'urlCallback'])
            && !strpos($value, 'secret=')) {

            return $value . (strpos($value, '?') ? '&' : '?') . 'secret=' . $webhook;
        }

        return $value;
    }