protected function call($url)
    {
        $scheme = 'https://';
        $host = 'openapi.bol.com';
        $content = '';
        $today = gmdate('D, d F Y H:i:s \G\M\T');
        $contentType =	'application/xml';

        $headers = array(
            'Content-type: ' . $contentType,
            'Host: ' . $host,
            'Content-length: ' . strlen($content),
            'X-OpenAPI-Authorization: ' . $this->getSignature($today, 'GET', $url, $contentType),
            'X-OpenAPI-Date: ' . $today,
        );
        if(!is_null($this->sessionId)) {
            $headers[] = 'X-OpenAPI-Session-ID: ' . $this->sessionId;
        }

        $response = $this->browser->get($scheme.$host.$url, $headers);
        if ($response->getStatusCode() === 503) {
            throw new BolException('Service Temporarily Unavailable', 503);
        }

        return $response;
    }