using System;

using System.Security.Cryptography;

using System.Text;

using System.Net.Http;

using System.Net.Http.Headers;

using System.Web;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main()

    {   

        var ClientId = "feb56dac-795b-4b98-89ce-53af2de61e60";

        var ClientSecret = "Lm05o23OdrPv71pEWajeJYWhQb2XdsfTELORo4NiewE=";

        var secretKeyByteArray = Convert.FromBase64String(ClientSecret);

        var requestUri = System.Web.HttpUtility.UrlEncode("http://entapistaging.shieldpay.com/v2/currencies"); // http%253a%252f%252fentapistaging.shieldpay.com%252fv2%252fcurrencies

        var requestTimeStamp = GetTimeStamp(); // "1556029203";

        var nonce = Guid.NewGuid().ToString("N"); // "94ce152de0df445d9a4d42ce1cee7a40";

        var bodyHash = string.Empty;

        var signatureRawData = String.Format("{0}{1}{2}{3}{4}{5}", ClientId, "GET", requestUri, requestTimeStamp, nonce, bodyHash);     

        Console.WriteLine(signatureRawData);

        var mac = Convert.ToBase64String(ComputeHash(Encoding.UTF8.GetBytes(signatureRawData), secretKeyByteArray)); // 9zQcAqy4i4aZkZQ1hANKgx9IIRsywjsNKXj2th2wV2s=

        Console.WriteLine(mac);

        var authHeaderValue = string.Format("organizationid={0},timestamp={1},nonce={2},bodyhash={3},mac={4}", ClientId, requestTimeStamp, nonce, bodyHash, mac);

        Console.WriteLine(authHeaderValue);

        var authHeaderValueArray = Encoding.ASCII.GetBytes(authHeaderValue);        

        var authHeader = Convert.ToBase64String(authHeaderValueArray); // b3JnYW5pemF0aW9uaWQ9ZmViNTZkYWMtNzk1Yi00Yjk4LTg5Y2UtNTNhZjJkZTYxZTYwLHRpbWVzdGFtcD0xNTU2MDI5MjAzLG5vbmNlPTk0Y2UxNTJkZTBkZjQ0NWQ5YTRkNDJjZTFjZWU3YTQwLGJvZHloYXNoPSxtYWM9OXpRY0FxeTRpNGFaa1pRMWhBTktneDlJSVJzeXdqc05LWGoydGgyd1Yycz0=

        Console.WriteLine("authorization " + authHeader);

        HttpRequestMessage request = new HttpRequestMessage();          

        request.Headers.Authorization = new AuthenticationHeaderValue("authorization", authHeader);     

    }

    private static byte[] ComputeHash(byte[] buffer, byte[] secretKeyByteArray)

            {

                using (HMACSHA256 hmactobody = new HMACSHA256(secretKeyByteArray))

                {

                    return hmactobody.ComputeHash(buffer);

                }

            }

    private static string GetTimeStamp()

            {

                DateTime epochStart = new DateTime(1970, 01, 01, 0, 0, 0, 0, DateTimeKind.Utc);

​

                TimeSpan timeSpan = DateTime.UtcNow - epochStart;

​

                return Convert.ToUInt64(timeSpan.TotalSeconds).ToString();

            }

}