using System;

using System.Text;

using System.Security.Cryptography;

​

public class Program

{

    private const string requestLine = "POST https://api.notserv.com/updates HTTP/1.1\r\n";

    private const string host = "api.notserv.com";

    private const string date = "Fri, 18 Sep 2020 08:57:24 GMT";

    private const string body = @"{

  ""data"": [

    {

      ""id"": ""8fb16f51-4955-4fa7-a926-e36ab9ecddf8"",

      ""type"": ""datapoint"",

      ""links"": {

        ""self"": ""/datapoints/8fb16f51-4955-4fa7-a926-e36ab9ecddf8""

      },

      ""attributes"": {

        ""value"": ""25.0"",

        ""timestamp"": ""2021-02-17T17:17:17.000Z""

      }

    },

    {

      ""id"": ""8fb16f51-4955-4fa7-a926-e36ab9ecddf9"",

      ""type"": ""datapoint"",

      ""links"": {

        ""self"": ""/datapoints/8fb16f51-4955-4fa7-a926-e36ab9ecddf9""

      },

      ""attributes"": {

        ""value"": ""on"",

        ""timestamp"": ""2021-02-17T17:17:17.000Z""

      }

    }

  ]

}";

    private static int contentLength_int = body.Length;

    private static string contentLength = Convert.ToString(contentLength_int, 10);

    private const string secret = "TheBestPasswordEver";

​

    private static string concatString = requestLine + host + date + contentLength + body;

    public static void Main()

    {

        var hash = GetHash(

            requestLine,

            host,

            date,

            contentLength,

            body,

            secret

        );

        Console.WriteLine("Hash: " + hash + "\n");

        Console.WriteLine("Content-Length: " + contentLength + "\n");

        Console.WriteLine("concatString:\n" + concatString);

    }

​

    private static string GetHash(string requestLine, // Includes CRLF end

 string host, string date, string contentLength, string body, string secret)

    {

        var stringToSign = requestLine + host + date + contentLength + body;

        using (var hmacsha256 = new HMACSHA256(Encoding.UTF8.GetBytes(secret)))

        {

            var bytes = Encoding.UTF8.GetBytes(stringToSign);

            var hashedBytes = hmacsha256.ComputeHash(bytes);

            return Convert.ToBase64String(hashedBytes);

        }

    }

}