private function addTrustedHosts($siteUrl)
    {
        $trustedHosts = array();

        // extract host from the request header
        if (($host = $this->extractHost('http://' . Url::getHost())) !== false) {
            $trustedHosts[] = $host;
        }

        // extract host from first web site
        if (($host = $this->extractHost(urldecode($siteUrl))) !== false) {
            $trustedHosts[] = $host;
        }

        $trustedHosts = array_unique($trustedHosts);
        if (count($trustedHosts)) {

            $general = Config::getInstance()->General;
            $general['trusted_hosts'] = $trustedHosts;
            Config::getInstance()->General = $general;

            Config::getInstance()->forceSave();
        }
    }