protected function _withCacheHeaders($response, $cacheTime, $modifiedTime)
    {
        $expire = strtotime($cacheTime);
        $maxAge = $expire - time();

        return $response
            ->withHeader('Cache-Control', 'public,max-age=' . $maxAge)
            ->withHeader('Date', gmdate('D, j M Y G:i:s \G\M\T', time()))
            ->withHeader('Last-Modified', gmdate('D, j M Y G:i:s \G\M\T', (int)$modifiedTime))
            ->withHeader('Expires', gmdate('D, j M Y G:i:s \G\M\T', $expire));
    }