private function sign($data, $algorithm)
{
if ($algorithm === 'HmacSHA1') {
$hash = 'sha1';
} else {
if ($algorithm === 'HmacSHA256') {
$hash = 'sha256';
} else {
throw new \Exception("Non-supported signing method specified");
}
}
return base64_encode(hash_hmac($hash, $data, $this->config['secret_key'], true));
}