kf_curl

    public function postJson($url, array $fields) {
        $client = curl_init();

        $data      = json_encode($fields);
        $headers   = $this->flattenHeaders();
        $headers[] = 'Content-Length: ' . strlen($data);

        // Default parameters
        curl_setopt_array($client, [
            CURLOPT_TIMEOUT        => 30,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_HTTPAUTH       => CURLAUTH_BASIC,
            CURLOPT_USERPWD        => $this->authHeader,
            CURLOPT_URL            => $this->buildUrl($url),
            CURLOPT_POST           => true,
            CURLOPT_POSTFIELDS     => $data,
            CURLOPT_HTTPHEADER     => $headers,
        ]);

        $body = curl_exec($client);

        if (curl_errno($client)) {
            throw new CurlException(curl_error($client), curl_errno($client));
        }

        $result = CurlResponse::factory($body, $client);

        curl_close($client);

        return $result;
    }