Simple tracking online users in ASP.NET

I wrote simple online users tracking for my ASP.NET MVC project.

1. In Global.asax I added:

   protected void Session_Start(Object sender, EventArgs e)
   {
       // get current context
       HttpContext currentContext = HttpContext.Current;
   
       if (currentContext != null)
       {
           if (!currentContext.Request.Browser.Crawler)
           {
               WebsiteVisitor currentVisitor = new WebsiteVisitor(currentContext);
               OnlineVisitorsContainer.Visitors[currentVisitor.SessionId] = currentVisitor;
           }
       }
   }
   
   protected void Session_End(Object sender, EventArgs e)
   {
       // Code that runs when a session ends.
       // Note: The Session_End event is raised only when the sessionstate mode
       // is set to InProc in the Web.config file. If session mode is set to StateServer
       // or SQLServer, the event is not raised.
   
       if (this.Session != null)
       {
           WebsiteVisitor visitor;
           OnlineVisitorsContainer.Visitors.TryRemove(this.Session.SessionID, out visitor);
       }
   }
   
   protected void Application_PreRequestHandlerExecute(object sender, EventArgs eventArgs)
   {
       var session = HttpContext.Current.Session;
       if (session != null && HttpContext.Current.User != null && HttpContext.Current.User.Identity.IsAuthenticated)
       {
           if (OnlineVisitorsContainer.Visitors.ContainsKey(session.SessionID))
           OnlineVisitorsContainer.Visitors[session.SessionID].AuthUser = HttpContext.Current.User.Identity.Name;
       }
   }
   

2. Here is my WebsiteVisitor class:

   using System;
   using System.Collections.Concurrent;
   using System.Collections.Generic;
   using System.Web;
   
   namespace WebApplication.Areas.Admin.Models
   {
       public class WebsiteVisitor
       {
           public string SessionId { get; set; }
   
           public string IpAddress { get; set; }
   
           public string AuthUser { get; set; }
   
           public string UrlReferrer { get; set; }
   
           public string EnterUrl { get; set; }
   
           public string UserAgent { get; set; }
   
           public DateTime SessionStarted { get; set; }
   
           public WebsiteVisitor(HttpContext context)
           {
               if (context != null && context.Request != null && context.Session != null)
               {
                   this.SessionId = context.Session.SessionID;
   
                   this.SessionStarted = DateTime.UtcNow;
   
                   //this.UserAgent = String.IsNullOrEmpty(context.Request.UserAgent) ? "" : context.Request.UserAgent;
                   this.UserAgent = context.Request.UserAgent ?? String.Empty;
   
                   this.IpAddress = context.Request.UserHostAddress;
   
                   //-------------------------------------------------------------
                   if (context.Request.IsAuthenticated)
                   {
                       this.AuthUser = context.User.Identity.Name;
                       if (!String.IsNullOrEmpty(context.Request.ServerVariables["REMOTE_USER"]))
                       this.AuthUser = context.Request.ServerVariables["REMOTE_USER"];
                       else if (!String.IsNullOrEmpty(context.Request.ServerVariables["AUTH_USER"]))
                       this.AuthUser = context.Request.ServerVariables["AUTH_USER"];
                   }
   
                   //-------------------------------------------------------------
                   if (context.Request.UrlReferrer != null)
                   {
                       this.UrlReferrer = String.IsNullOrWhiteSpace(context.Request.UrlReferrer.OriginalString) ? "" : context.Request.UrlReferrer.OriginalString;
                   }
   
                   this.EnterUrl = String.IsNullOrWhiteSpace(context.Request.Url.OriginalString) ? "" : context.Request.Url.OriginalString;
               }
           }
       }
   
       /// <summary>
       /// Online visitors list
       /// </summary>
       public static class OnlineVisitorsContainer
       {
           public static readonly ConcurrentDictionary<string, WebsiteVisitor> Visitors = new ConcurrentDictionary<string, WebsiteVisitor>();
       }
   }
   

3. And the last step is to write Action method in controller and display this data in view:

   public ActionResult WhoIsOnline()
   {
       if (OnlineVisitorsContainer.Visitors != null)
       {   
           return View(OnlineVisitorsContainer.Visitors.Values.OrderByDescending(x => x.SessionStarted));
       }
   
       return HttpNotFound();
   }
   

Do you see any improvement / issue?