$url_parts = parse_url($url);

$canonical_url = ($url_parts['path'] . (!empty($url_parts['query']) ? "?${url_parts['query']}" : ""));

$message = $http_method."\n".

    $canonical_url."\n".

    $timestamp."\n".

    $nonce."\n".

    $body."\n";

openssl_sign($message, $raw_sign, $mch_private_key, 'sha256WithRSAEncryption');

$sign = base64_encode($raw_sign);