c# version

using Newtonsoft.Json.Linq;
using System;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Threading.Tasks;

namespace Citi.QSDB.WebApi.Client
{
public class QSDBAPIAgent
{
private readonly string userName;
private readonly string password;
private readonly string baseUrl;
private string tokenString;
private string tokenExpiry;

    static QSDBAPIAgent()
    {
        // for ignoring DEV/UAT server cert alert, not required in PROD
        var trustAllCerts = new X509Certificate2Collection();
        ServicePointManager.ServerCertificateValidationCallback = (sender, cert, chain, sslPolicyErrors) => true;
    }

    public QSDBAPIAgent(string baseUrl, string userName, string password)
    {
        if (string.IsNullOrEmpty(userName))
            throw new ArgumentException("userName is null");
        if (string.IsNullOrEmpty(password))
            throw new ArgumentException("password is null");

        this.userName = userName;
        this.password = password;
        this.baseUrl = baseUrl;
    }

    public async Task<string> LoadData(string requestUrl)
    {
        if (!IsTokenExpiryValid())
            await ApplyNewToken();

        using (var client = new HttpClient())
        {
            var requestUri = new Uri(baseUrl + requestUrl);
            client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", tokenString);
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            var response = await client.GetAsync(requestUri);

            if (!response.IsSuccessStatusCode)
                throw new Exception("Load data failed with url " + baseUrl + requestUrl);

            return await response.Content.ReadAsStringAsync();
        }
    }

    public bool IsTokenExpiryValid()
    {
        if (string.IsNullOrEmpty(tokenString))
            return false;

        var instant = Instant.Parse(tokenExpiry);
        var compareResult = instant.Minus(Duration.OfMinutes(30)).CompareTo(Instant.Now);
        return compareResult < 0;
    }

    private async Task ApplyNewToken()
    {
        using (var client = new HttpClient())
        {
            var requestUri = new Uri(baseUrl + "/qsdb/api/rest/auth/v1/token");
            var requestBody = "{\"Username\":\"" + userName + "\",\"Password\":\"" + password + "\"}";

            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            var response = await client.PostAsync(requestUri, new StringContent(requestBody, Encoding.UTF8, "application/json"));

            if (!response.IsSuccessStatusCode)
                throw new AuthenticationException("Authenticate failed");

            var responseString = await response.Content.ReadAsStringAsync();
            var jsonObject = JObject.Parse(responseString);
            tokenString = jsonObject.GetValue("TokenString").ToString();
            tokenExpiry = jsonObject.GetValue("TokenExpiry").ToString();

            if (string.IsNullOrEmpty(tokenString) || string.IsNullOrEmpty(tokenExpiry))
                throw new AuthenticationException("Authenticate failed");
        }
    }

    public class AuthenticationException : Exception
    {
        public AuthenticationException() { }
        public AuthenticationException(string message) : base(message) { }
        public AuthenticationException(string message, Exception innerException) : base(message, innerException) { }
    }
}

}