public function config($newConfig = null)
    {
        if ($newConfig === null) {
            return $this->clientConfig;
        }

        $this->clientConfig = $this->initConfig($newConfig);

        $this->httpClient = new HttpClient([
            'base_uri' => $this->clientConfig['url'],
            'timeout' => $this->clientConfig['timeout'],
            'handler' => $this->clientConfig['handler'],
        ]);

        return $this;
    }