Detecting Session expiry on ASP.NET MVC

The King 's answer does not work for me. I have added FormsAuthentication.SignOut() in OnActionExcuting(). The Response.Redirect will not work!

if (Request.IsAuthenticated)
{
    FormsAuthentication.SignOut();
}

This is my complete method

public class SessionExpireFilterAttribute : ActionFilterAttribute
    {

        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            HttpContext ctx = HttpContext.Current;

            // check if session is supported
            if (ctx.Session != null)
            {

                // check if a new session id was generated
                if (ctx.Session.IsNewSession)
                {

                    // If it says it is a new session, but an existing cookie exists, then it must
                    // have timed out
                    string sessionCookie = ctx.Request.Headers["Cookie"];
                    if ((null != sessionCookie) && (sessionCookie.IndexOf("ASP.NET_SessionId") >= 0))
                    {
                        string redirectOnSuccess = filterContext.HttpContext.Request.Url.PathAndQuery;
                        string redirectUrl = string.Format("?ReturnUrl={0}", redirectOnSuccess);
                        string loginUrl = FormsAuthentication.LoginUrl + redirectUrl;
                        if (ctx.Request.IsAuthenticated)
                        {
                            FormsAuthentication.SignOut();
                        }
                        RedirectResult rr = new RedirectResult(loginUrl);
                        filterContext.Result = rr;
                        //ctx.Response.Redirect("~/Home/Logon");

                    }
                }
            }

            base.OnActionExecuting(filterContext);
        }
    }

Way 1

Put this code in the Init / Load event of Page 2...

        if (Context.Session != null)
        {
            if (Context.Session.IsNewSession)
            {
                string sCookieHeader = Request.Headers["Cookie"];
                if ((null != sCookieHeader) && (sCookieHeader.IndexOf("ASP.NET_SessionId") >= 0))
                {

                    if (Request.IsAuthenticated)
                    {
                        FormsAuthentication.SignOut();
                    }
                    Response.Redirect("Error Page");
                }
            }
        }

Way 2

Alternative you can check whether the Session object exists before proceeding to work with it in Page 2, like this:

if (Session["Key"] != null)
{
   Object O1 = (Object) Session["Key"]; 
}
else
{
    Response.Redirect("ErrorPage.aspx");
}