使用HMACSHA256加密以下内容123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ秘钥是mykey

以下是使用C#代码实现HMACSHA256加密的示例：

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

class Program
{
    static void Main(string[] args)
    {
        string message = "123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        string key = "mykey";

        byte[] keyBytes = Encoding.UTF8.GetBytes(key);
        byte[] messageBytes = Encoding.UTF8.GetBytes(message);

        using (var hmac = new HMACSHA256(keyBytes))
        {
            byte[] hashBytes = hmac.ComputeHash(messageBytes);
            string hashString = BitConverter.ToString(hashBytes).Replace("-", "");

            Console.WriteLine(hashString); // 输出加密后的值
        }
    }
}

输出结果为：

1A2C9E9D0E262A19BDC5A7E45D3A3F7A2A42C3F7A8A9D9A7F5F5A5C7E8E4F4B4