public function getKey($keyname = self::DEFAULT_KEY)
    {
        if (!isset($this->_keyCache[$keyname])) {
            if (isset($_COOKIE[$keyname . '_key'])) {
                $key = $_COOKIE[$keyname . '_key'];
            } else {
                $key = session_id();
                $this->_setCookie($keyname, $key);
            }

            $this->_keyCache[$keyname] = $key;
        }

        return $this->_keyCache[$keyname];
    }