抖音退款接口:https://developer.toutiao.com/api/apps/ecpay/v1/create_refund 的签名方式请用.net代码写一个方法

以下是使用C#语言编写的抖音退款接口签名方法：

using System;
using System.Security.Cryptography;
using System.Text;

public static string GenerateSignature(string appid, string secret, long timestamp, string refundId, string orderId, int refundAmount, int refundReasonId, string refundReasonInfo)
{
    // 将参数按照字典序排序
    var sortedParams = new SortedDictionary<string, string>
    {
        { "app_id", appid },
        { "refund_id", refundId },
        { "order_id", orderId },
        { "refund_amount", refundAmount.ToString() },
        { "refund_reason_id", refundReasonId.ToString() },
        { "refund_reason_info", refundReasonInfo },
        { "timestamp", timestamp.ToString() }
    };

    // 拼接参数字符串
    var paramString = new StringBuilder();
    foreach (var item in sortedParams)
    {
        paramString.Append(item.Key).Append("=").Append(item.Value).Append("&");
    }
    paramString.Append("app_secret=").Append(secret);

    // 计算签名
    var sha256 = SHA256.Create();
    var hashBytes = sha256.ComputeHash(Encoding.UTF8.GetBytes(paramString.ToString()));
    var signature = Convert.ToBase64String(hashBytes);

    return signature;
}

该方法接受以下参数：

- `appid`：开发者应用唯一标识符
- `secret`：开发者应用密钥
- `timestamp`：当前时间戳，单位为秒
- `refundId`：退款单号
- `orderId`：原订单号
- `refundAmount`：退款金额，单位为分
- `refundReasonId`：退款原因编号
- `refundReasonInfo`：退款原因描述

该方法返回一个字符串，表示计算得到的签名值。