using System;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public static void Main()

    {

        string sso_key = "ABCD/EXAMPLE+SUPPLIER+KEY/0123456789/0123456789/FOR+TESTING+ONLY/0123456789/0123456789==";

        string expiry = "2014-06-24T09:30:00Z";

        string nonce = "000/NONCE+TEST/123456789";

        string url = "http://steadfast-supplier.example.com/some-page";

        string user = "john@broker.example.com";

        byte[] key = Convert.FromBase64String(sso_key);

        string message = expiry + '|' + nonce + '|' + url  + '|' + user;

        byte[] hmac;

        using (HMACSHA1 hmacAlgorithm = new HMACSHA1(key))

        {

            hmac = hmacAlgorithm.ComputeHash(Encoding.UTF8.GetBytes(message));

        }

​

        Console.WriteLine("Message: " + message);

        Console.WriteLine("HMAC: " + Convert.ToBase64String(hmac));

        Console.WriteLine("Expected HMAC: wmxQPMXbD0bx3sKU5uhfKlXtg7A=");

    }

}