public function requestAsync($method, $url, $body = [], $query = [], $headers = [])
    {
        if (!empty($body)) {
            $body = encode($body);
            $headers['Content-Type'] = 'application/json';
        } else {
            $body = null;
        }

        $headers = array_merge($this->global_headers, $headers);

        return $this->client->requestAsync($method, $url, [
            'query'   => $query,
            'body'    => $body,
            'headers' => $headers,
        ]);
    }