OC Hash

using System;
    using System.Security.Cryptography;
class MainClass {
    static void Main() {
        
        var apiKey = "67d594c6-9312-4df8-9b21-952cfdff1617";
        
        var payload = new AuthenticationPayload
        {
            SourceSystemId = 1,
            SourceSystemScenarioId = 1,
            ReferenceId = "46436",
            Nonce = Guid.NewGuid().ToString()
        };
        
        var hashCalc = new HashCalculator();
        
        Console.WriteLine(payload.Nonce);
        
        Console.WriteLine(hashCalc.CalculateHash(apiKey, payload.AsHashAuthenticationString));
    }
}

    public class AuthenticationPayload
    {
        public int SourceSystemId { get; set; }
        public int SourceSystemScenarioId { get; set; }
        public string ReferenceId { get; set; }
        public string Nonce { get; set; }
        public string AsHashAuthenticationString => $"{SourceSystemId}:{SourceSystemScenarioId}:{ReferenceId}:{Nonce}";

    }

public class HashCalculator
    {

        public string CalculateHash(string key, string computedAuthenticationString)
        {
            if (string.IsNullOrWhiteSpace(key) || string.IsNullOrWhiteSpace(computedAuthenticationString))
            {
                return "";
            }

            var encoding = new System.Text.UTF8Encoding();

            try
            {
                var keyByte = encoding.GetBytes(key);

                var computedAuthenticationBytes = System.Text.Encoding.UTF8.GetBytes(computedAuthenticationString);
                var encodedAuthenticationString = Convert.ToBase64String(computedAuthenticationBytes);

                var computedHash = "";

                using (var hmacsha256 = new HMACSHA256(keyByte))
                {
                    var encodedAuthenticationStringBytes = encoding.GetBytes(encodedAuthenticationString);

                    var hashmessage = hmacsha256.ComputeHash(encodedAuthenticationStringBytes);

                    computedHash = ByteToString(hashmessage);
                }

                return computedHash;
            }
            catch (Exception ex)
            {
                return "";
            }
        }
        private string ByteToString(byte[] buff)
        {
            string sbinary = "";

            for (int i = 0; i < buff.Length; i++)
            {
                sbinary += buff[i].ToString("X2");
            }

            return (sbinary);
        }
    }