access to a website(c#) from a class library and avoid .NET login

Example

//GET COOKIE
var authCookie = _loginHelper.GetAuthCookie(email, password);

//SERIELIZE JSON 
var jsonDetails = JsonConvert.SerializeObject(details);

//RESPONSE
var response = _portfolioHelper.HttpPost( _path, jsonDetails, authCookie);
var result = JsonConvert.DeserializeObject<Response<int?>>(response);

HttpHelper

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;

namespace Project.Helpers
{
    public class HttpHelper
    {
        public HttpHelper() { }

        public string HttpPost(string path, string json, Cookie authCookie)
        {
            var request = (HttpWebRequest)HttpWebRequest.Create(path);
            //Proxy credentials
            var proxy = WebRequest.DefaultWebProxy;
            if (proxy != null)
            {
                request.Proxy = proxy;
                request.Credentials = CredentialCache.DefaultNetworkCredentials;
                request.Proxy.Credentials = CredentialCache.DefaultNetworkCredentials;
            }
            request.Method = "POST";
            var cookieJar = new CookieContainer();
            cookieJar.Add(authCookie);
            request.CookieContainer = cookieJar;
            request.ContentType = "application/json";

            // write body
            using (var streamWriter = new StreamWriter(request.GetRequestStream()))
            {
                streamWriter.Write(json);
                streamWriter.Flush();
                streamWriter.Close();
            }
            
            // send request
            var webResponse = request.GetResponse() as HttpWebResponse;
            using (Stream stream = webResponse.GetResponseStream())
            {
                StreamReader reader = new StreamReader(stream, Encoding.UTF8);
                String responseString = reader.ReadToEnd();
                return responseString;
            }
        }

        public string HttpGet(string path, Cookie authCookie)
        {
            var request = (HttpWebRequest)HttpWebRequest.Create(path);
            
            //Proxy credentials
            var proxy = WebRequest.DefaultWebProxy;
            if (proxy != null)
            {
                request.Proxy = proxy;
                request.Credentials = CredentialCache.DefaultNetworkCredentials;
                request.Proxy.Credentials = CredentialCache.DefaultNetworkCredentials;
            }
            request.Method = "GET";
            var cookieJar = new CookieContainer();
            cookieJar.Add(authCookie);
            request.CookieContainer = cookieJar;
            var webResponse = request.GetResponse() as HttpWebResponse;
            using (Stream stream = webResponse.GetResponseStream())
            {
                StreamReader reader = new StreamReader(stream, Encoding.UTF8);
                String responseString = reader.ReadToEnd();
                return responseString;
            }
        }
    }
}

LoginHelper

using HtmlAgilityPack;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace Project.Helpers
{
    public class LoginHelper
    {

#if DEBUG 
        private const string _path = "your test path";
#else
        private const string _path = "your path";
#endif

        public LoginHelper() { }

        public Cookie GetAuthCookie(string email, string password)
        {
            var postData = String.Format("Email={0}&Password={1}&RememberMe={2}", email, password, false);
            var request = (HttpWebRequest)HttpWebRequest.Create(_path);
            request.AllowAutoRedirect = false;
            //Proxy credentials
            var proxy = WebRequest.DefaultWebProxy;
            if (proxy != null)
            {
                request.Proxy = proxy;
                request.Credentials = CredentialCache.DefaultNetworkCredentials;
                request.Proxy.Credentials = CredentialCache.DefaultNetworkCredentials;
            }
            request.Method = "POST";
            var cookieJar = new CookieContainer();
            request.CookieContainer = cookieJar;
            request.ContentLength = postData.Length;
            request.ContentType = "application/x-www-form-urlencoded";
            var myWriter = new StreamWriter(request.GetRequestStream());
            myWriter.Write(postData);
            myWriter.Close();
            var webResponse = request.GetResponse() as HttpWebResponse;
            var rawHeaders = request.GetResponse().Headers.ToString();
            return webResponse.Cookies[0];
        }
    }
}