Zamiana klucza w json

/**
     * replace user agent in text to user agent from actual environment
     * 
     * @param string $text
     * 
     * @return string
     */
    private function replaceUserAgent(string $text): string {
        $client = new Client();
        $userAgent = str_replace('/', '\/', ($client->getConfig('headers')['User-Agent']));

        $result = preg_replace('/"user_agent":"(Guzzle[A-Za-z0-9 . \/\\\]*)"/', '"user_agent":"' . $userAgent . '"', $text);

//or $result = preg_replace('/"user_agent":"GuzzleHttp(.*)"/', '"user_agent":"' . $userAgent . '"', $text);

//. kropka - dowolny znak * oznacza dowolną ilosc razy bez gwiazdki brało by pod uwagę tylko pierwszy znak.  

        return $result;
    }