using System;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public static void Main()

    {

        var key= Encoding.UTF8.GetBytes("kNMbuxZdP/Dh-9r8Btu[!!Tv686ULw");

        var message = Encoding.UTF8.GetBytes("3468+POST+/supplier-products/v1+2021-03-15-T16:28:00Z");

        using (var hmac = new HMACSHA1(key)){

            var hash = hmac.ComputeHash(message);

            var digest = Convert.ToBase64String(hash);

            Console.WriteLine(digest);

        }

    }

}

​

​