how to stop application asp.net with global.asax

I want to stop my application asp.net Mvc in Session_Start after a test and show to user that he isn't authorized for this application

 protected void Session_Start(object sender, EventArgs e)
 {
     if (test)
     {
         //stop application
         // say to user : not authorized
     }
 }

Finally i send a response and close the session and it works

protected void Session_Start(object sender, EventArgs e){
         if (test){
              ASCIIEncoding encoding = new ASCIIEncoding();
              string postData = "<h2 style=\"color:RED;\"Not authorized!!</h2>. ";
              byte[] data = encoding.GetBytes(postData);
              char[] buf = postData.ToCharArray();
              HttpContext.Current.Response.Write(buf, 0, buf.Count());
              HttpContext.Current.Response.Flush();
              HttpContext.Current.ApplicationInstance.CompleteRequest();
              Session.Abandon();
         }
     }