PayWithAmazon\Client::sign PHP Method

    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));
    }