签名计算过程（C# 版本）

<p>string rawData = $&quot;{req.merchantid}{req.user_name}{req.timestamp}&quot;;</p> <p>using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(mer.Apikey));</p> <p>byte[] hashBytes = hmac.ComputeHash(Encoding.UTF8.GetBytes(rawData));</p> <p>string computedSignature = Convert.ToHexString(hashBytes).ToLower();</p>