JsonRpcClient

example.php

<?php
define('API', 'https://HOST/api');
define('USERNAME', '******');
define('PASSWORD', '******');

$client = new SimpleJsonRpcClient(API);
$result = $client->login(['username' => USERNAME, 'password' => PASSWORD]);
$client->setAuthToken($result->token);

$result = $client->{'product.sell'}(['id' => 1, 'price' => 100]);

class SimpleJsonRpcClient
{
    private $id;
    protected $endpoint;
    private $authToken;
    public function __construct($endpointUrl) {
        $this->endpoint  = $endpointUrl;
        $this->id = 0;
    }
    public function setAuthToken($authToken)
    {
        $this->authToken = $authToken;
    }
    protected function _requestFactory($method, $args) {
        $request = new stdClass;
        $request->jsonrpc = '2.0';
        $request->method = $method;
        $request->params = $args;
        $request->id = $this->id++;
        return json_encode($request);
    }
    protected function _curlFactory($data) {
        $options = array(
            CURLOPT_FRESH_CONNECT => false,
            CURLOPT_POST => true,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_POSTFIELDS => $data,
        );
        if ($this->authToken) {
            $options[CURLOPT_HTTPHEADER] = ['X-Auth-Token: '.$this->authToken];
        }
        $curl = curl_init($this->endpoint);
        curl_setopt_array($curl, $options);
        return $curl;
    }
    public function __call($method, $args) {
        $request = $this->_requestFactory($method, (object) $args[0]);
        $curl    = $this->_curlFactory(json_encode($request));
        $raw     = curl_exec($curl);
        $return  = json_decode($raw);
        curl_close($curl);
        if(isset($return->error)) {
            throw new Exception($return->error->message, $return->error->code);
        }
        return $return->result;
    }
}