using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(GetUserIdentityHash(123) == "4839c3ddf0b2d28b26ee9d6ba9e46701e7e46ce57ccc518ffc70f33274edc18e");

    }

     public static string GetUserIdentityHash(int userId) {               

            byte[] secretKey = System.Text.Encoding.UTF8.GetBytes("SA6ZOZZRbxpbyjeLlH5uY-yhXeGQa72utowzM7XD");

            byte[] bytes = System.Text.Encoding.UTF8.GetBytes(userId.ToString());

            using (var hmac = new System.Security.Cryptography.HMACSHA256(secretKey))

            {

                hmac.ComputeHash(bytes);

                // Return the hexadecimal string.

                return String.Concat(hmac.Hash.Select(x => x.ToString("x2")));

            }        

        }

}