using System;

using System.Net.Http;

using System.Security.Cryptography;

using System.Web;

public class Program

{

    public static void Main()

    {

        var url = "";

        var privateKey = "";

        var publicKey = "";

        var method = "GET";

        HttpContent content = null;

        var header = GetHeaderValue(method, url, content, privateKey, publicKey);

        Console.WriteLine(header);

    }

private static string GetHeaderValue(string requestHttpMethod, string requestAbsoluteUri, HttpContent httpContent, string privateKey, string publicKey)

{

    string requestContentBase64String = string.Empty;

​

    string requestUri = HttpUtility.UrlEncode(requestAbsoluteUri.ToLower());

​

    //Calculate UNIX time

    DateTime epochStart = new DateTime(1970, 01, 01, 0, 0, 0, 0, DateTimeKind.Utc);

    TimeSpan timeSpan = DateTime.UtcNow - epochStart;

    string requestTimeStamp = Convert.ToUInt64(timeSpan.TotalSeconds).ToString();

​

    //create random nonce for each request

    string nonce = Guid.NewGuid().ToString("N");

​

    //Checking if the request contains body, usually will be null wiht HTTP GET and DELETE

    if (httpContent != null)

    {

        //byte[] content = await request.Content.ReadAsByteArrayAsync();

        byte[] content = httpContent.ReadAsByteArrayAsync().Result;

        MD5 md5 = MD5.Create();

​

        //Hashing the request body, any change in request body will result in different hash, we'll incure message integrity

        byte[] requestContentHash = md5.ComputeHash(content);

        requestContentBase64String = Convert.ToBase64String(requestContentHash);

    }

​

    //Creating the raw signature string

    string signatureRawData = $"{publicKey}{requestHttpMethod}{requestUri}{requestTimeStamp}{nonce}{requestContentBase64String}";

​

    var secretKeyByteArray = Convert.FromBase64String(privateKey);

​

    byte[] signature = System.Text.Encoding.UTF8.GetBytes(signatureRawData);

​

    using (HMACSHA256 hmac = new HMACSHA256(secretKeyByteArray))

    {

        byte[] signatureBytes = hmac.ComputeHash(signature);

        string requestSignatureBase64String = Convert.ToBase64String(signatureBytes);

​

        //Setting the values in the Authorization header using custom scheme (amx)

        var headerValue = $"amx {publicKey}:{requestSignatureBase64String}:{nonce}:{requestTimeStamp}";

        return headerValue;    

     }

}

​

​

}