using System;

using System.Collections.Generic;

using System.Linq;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public const string APIKey = "";

    public static void Main()

    {

        if(string.IsNullOrEmpty(APIKey))

        {

            throw new Exception("-- Set the API key above --");

        }

​

        var values = new Dictionary<string, string>() {

            { "x_account_id", "30139741"},

            { "x_amount", "1179"},

            { "x_currency", "AUD"},

            { "x_gateway_reference", "75046068"},

            { "x_purchase_number", "75046068"},

            { "x_reference", "4211346"},

            { "x_result", "completed"},

            { "x_test", "False"},

            { "x_timestamp", "2022-02-21T04:17:46Z"},

        };

        var hmac = GenerateHmac(values);

        Console.WriteLine("Generated:" + hmac);

        Console.WriteLine("Expecting:8c15700cc8a269f2c64eebe94bdfe098613d839fbc1eab9b4ca949f4f0569560");

    }

    public static string GenerateHmac(IDictionary<string, string> payloadValues)

    {

        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(APIKey));

​

        var payloadSignature =

            payloadValues

            .Where(kvp => kvp.Key != "x_signature" && kvp.Key.StartsWith("x_"))

            .OrderBy(kvp => kvp.Key)

            .Select(kvp => $"{kvp.Key}{kvp.Value}")

            .Aggregate((current, next) => $"{current}{next}");

        Console.WriteLine(payloadSignature);

​

        var rawHmac = hmac.ComputeHash(Encoding.UTF8.GetBytes(payloadSignature));

        return BitConverter.ToString(rawHmac).Replace("-", string.Empty).ToLower();

    }

}