using System;

using System.Security.Cryptography;

using System.Text;

using System.Linq;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var customerAccountNumber = "Checkout-3";

        var msisdn = "971525944760";

        var operatorCode = "42403";

        var subscriptionPlanId = "3";

        var initialPaymentproductId = "2021-10-05 12:56:52Z";

        var executeInitialPaymentNow = "false";

        var executeRecurringPaymentNow = "false";

        var recurringPaymentproductId = "T1";

        var productCatalogName = "HETest";

        var autoRenewContract = "true";

        var contractStartDate = "2021-09-29 12:56:52Z";

        var contractEndDate = "2031-09-29 12:56:52Z";

        var language = "2";

        var allowMultipleFreeStartPeriods = "";

​

        const string PublicKey = "0oa70WuefiddqLjqlTlp";

        const string PrivateKey = "m2vQxqNixqrEDcQ2heVr";

        var message =  customerAccountNumber

                                   + msisdn

                                   + operatorCode

                                   + subscriptionPlanId

                                   + initialPaymentproductId

                                   + executeInitialPaymentNow.ToString().ToLower()

                                   + recurringPaymentproductId

                                   + productCatalogName

                                   + executeRecurringPaymentNow.ToString().ToLower()

                                   + contractStartDate

                                   + contractEndDate

                                   + autoRenewContract.ToString().ToLower()

                                   + language

                                   + allowMultipleFreeStartPeriods;

        var theDigest = CalculateDigest(PublicKey, PrivateKey, message);

        Console.WriteLine(theDigest);

    }

​

    public static string CalculateDigest(string publicKey, string privateKey, string message)

    {

        var digest = "";

        var hash = new System.Security.Cryptography.HMACSHA256(System.Text.Encoding.UTF8.GetBytes(privateKey));

        var correctHash = string.Join(string.Empty, hash.ComputeHash(System.Text.Encoding.UTF8.GetBytes(message)).Select(b => b.ToString("x2")));

        digest = publicKey + ":" + correctHash;

        return digest;

    }

}