using System;

using System.Collections.Generic;

using System.Text;

using System.Security.Cryptography;

using Newtonsoft.Json;

using System.Net;

​

public class Program

{

    static string GetHmacHash(string input, string secret)

    {

        if (string.IsNullOrWhiteSpace(input)) return "";

        Encoding encoding = Encoding.UTF8;

        byte[] keyByte = encoding.GetBytes(secret);

        byte[] messageBytes = encoding.GetBytes(input);

​

        using (HMACSHA256 hmacsha256 = new HMACSHA256(keyByte))

        {

            byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);

            return BitConverter.ToString(hashmessage).Replace("-", "").ToLower();

        }

    }

​

    public static void Main()

    {

        var signatureKey = "DTest";

        var signatureHeader = "t=1669794735,hmac_sha256=8b915c6baf2e6c3fe1deeebdd9d39d736c4f1345f23dee07129770cc00d93cfb";

        var signature = new Dictionary<string, string>();

        foreach (var pair in signatureHeader.Split(',')) {

            var d = pair.Split('=');

            signature[d[0]] = d[1];

        }

        var requestString = "{'data':{'client':{'paymentInitiations':{'eventId':'90400463-ab37-4cab-8ced-da724015e0a5','subscriptionId':'YmFhNTNhYmUtZTViOC00M2UyLWEzMGQtZTZlNTE4OGZjZGJl','time':'2022-11-30T07:52:15.498Z','node':{'id':'cGF5aW5pdC9hOGZhMzc5Yy1iMmFhLTQ2NjYtOTEzZS1hZGY2MmRkYzU4ODc=','externalReference':'SM20221130834269794718967','beneficiaryReference':'10008685','date':'2022-11-30T07:52:15.074Z','status':{'__typename':'PaymentInitiationCompleted','date':'2022-11-30T07:52:15.238Z','payer':{'__typename':'PaymentInitiationBankAccountPayer','accountName':'FNB Premier Cheque Account','accountType':'current','accountNumber':'62120098985','bankId':'fnb'}}}}}}}";

        var request = JsonConvert.DeserializeObject(requestString);

        string body = JsonConvert.SerializeObject(request);

        string hashComputeInput = signature["t"] + "." + body;

        string computedHash = GetHmacHash(hashComputeInput, signatureKey);

​

        var incomingHash = signature.GetValueOrDefault("hmac_sha256");

        if (computedHash == incomingHash)

        {

            Console.WriteLine("Computed hash and incoming hash match");

        } else {

            throw new WebException($"Could not match computed {computedHash} with incoming {incomingHash}");

        }

    }

}