public function getServerLoginURL($gateway=false,$renew=false)
    {
        phpCAS::traceBegin();
        // the URL is build only when needed
        if ( empty($this->_server['login_url']) ) {
            $this->_server['login_url'] = $this->_buildQueryUrl($this->_getServerBaseURL().'login','service='.urlencode($this->getURL()));
        }
        $url = $this->_server['login_url'];
        if ($renew) {
            // It is recommended that when the "renew" parameter is set, its
            // value be "true"
            $url = $this->_buildQueryUrl($url, 'renew=true');
        } elseif ($gateway) {
            // It is recommended that when the "gateway" parameter is set, its
            // value be "true"
            $url = $this->_buildQueryUrl($url, 'gateway=true');
        }
        phpCAS::traceEnd($url);
        return $url;
    }