gistfile1.cs

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Net;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication2
{
    class Program
    {
        private static string domain = "*********.luna.akamaiapis.net";
        private static string secret = "*********";
        private static string access_token = "********";
        private static string client_token = "********";

        static void Main(string[] args)
        {
            string authorization_header = createAuthHeader("GET", "https", domain, "/alerts/v1/portal-user?status=active");

            using (WebClient client = new WebClient())
            {
                try
                {
                    client.Headers.Add("Authorization", authorization_header);
                    
                    NameValueCollection qs = new NameValueCollection();
                    qs.Add("status", "active");
                    client.QueryString = qs;
                    string result = client.DownloadString("https://" + domain + "/alerts/v1/portal-user");
                    Console.Write(result);
                }
                catch (WebException e)
                {
                    if (e.Status == WebExceptionStatus.ProtocolError)
                    {
                        Console.WriteLine("Status Code : {0}", ((HttpWebResponse)e.Response).StatusCode);
                        Console.WriteLine("Status Description : {0}", ((HttpWebResponse)e.Response).StatusDescription);
                    }
                }                
            }

            Console.ReadKey();
        }

        static string CreateToken(string message, string secret)
        {
            byte[] keyByte = Encoding.UTF8.GetBytes(secret);
            byte[] messageBytes = Encoding.UTF8.GetBytes(message);
            using (var hmacsha256 = new HMACSHA256(keyByte))
            {
               var hashmessage = hmacsha256.ComputeHash(messageBytes);
               return Convert.ToBase64String(hashmessage);
            }
        }

        static string createAuthHeader(string method,string scheme,string host,string path)
        {
            Guid guidValue = Guid.NewGuid();
            string timestamp = DateTime.Now.ToUniversalTime().ToString("yyyyMMddTHH:mm:ss+0000");
            string nonce = guidValue.ToString();

            string signing_key = CreateToken(timestamp, secret);

            string authorization_header = "EG1-HMAC-SHA256 ";
            authorization_header += "client_token=" + client_token + ";";
            authorization_header += "access_token=" + access_token + ";";
            authorization_header += "timestamp=" + timestamp + ";";
            authorization_header += "nonce=" + nonce + ";";

            string[] dataToSign = { method, scheme, host, path, "", "", authorization_header };

            string signature = CreateToken(String.Join("\t", dataToSign).Trim(), signing_key);

            authorization_header += "signature=" + signature;

            return authorization_header;
        }
    }
}