public function addLogger($logger, $format = 'CLF')
    {
        if (defined('GuzzleHttp\Subscriber\Log\Formatter::'.$format)) {
            $format = constant('GuzzleHttp\Subscriber\Log\Formatter::'.$format);
        }

        $subscriber = new LogSubscriber($logger, $format);
        $this->guzzleClient->getEmitter()->attach($subscriber);
    }