protected function discardCookie ($cookie)
    {
        if (!isset($cookie['domain'])
            || !isset($cookie['path'])
            || !isset($cookie['path'])
        ) {
            throw new CAS_InvalidArgumentException('Invalid Cookie array passed.');
        }

        foreach ($this->_cookies as $key => $old_cookie) {
            if ( $cookie['domain'] == $old_cookie['domain']
                && $cookie['path'] == $old_cookie['path']
                && $cookie['name'] == $old_cookie['name']
            ) {
                unset($this->_cookies[$key]);
            }
        }
    }