forms authentication cookie replacement

Question

I have a problem with users being kicked out after the forms authentication ticket is renewed and the old one has expired. The first ticket i get when i signed in is:

Ticket: A094D6F0401A5B6D97688198B09F17B03D209............ Ends: Thu, 28 Mar 2013 08:56:33 GMT

And after some time the ticket is renewed and i get this cookie: (The cookie expire when the ticket is expire, so no problem there)

Ticket: 215373E662852AD0CC540AC27F547787............. Ends: Thu, 28 Mar 2013 08:58:17 GMT

This ticket is renewed by a javascript reloader in the background for the user. Now, if i update the page, i will be kicked out, why? When i renew the ticket i use this:

        var Id = (FormsIdentity)HttpContext.Current.User.Identity;
        var Ticket = Id.Ticket;

        var NewAuthTicket = FormsAuthentication.RenewTicketIfOld(Ticket);

        HttpContext.Current.User = new System.Security.Principal.GenericPrincipal(new FormsIdentity(NewAuthTicket), new[] {""});

        if (NewAuthTicket != null && NewAuthTicket.Expiration > Ticket.Expiration)
        {
            // Create the (encrypted) cookie.
            var ObjCookie = new HttpCookie(FormsAuthentication.FormsCookieName,
                                           FormsAuthentication.Encrypt(NewAuthTicket))
                                {
                                    HttpOnly = true,
                                    Expires = NewAuthTicket.Expiration,
                                    Secure = FormsAuthentication.RequireSSL
                                };
            // Add the cookie to the list for outbound response. 
            HttpContext.Current.Response.Cookies.Add(ObjCookie);
            Ticket = NewAuthTicket;
         }

Is there any solution for this?

UPDATE:

When i set the cookie for the first time i use this:

var ExpiryDate = !rememberMe ? DateTime.Now.AddMinutes(cookieTimeoutHour) : DateTime.Now.AddYears(1);

                //create a new forms auth ticket
                var Ticket = new FormsAuthenticationTicket(2, ui.UserNr.ToString(CultureInfo.InvariantCulture), DateTime.Now, ExpiryDate, true, String.Empty);
                //encrypt the ticket
                var EncryptedTicket = FormsAuthentication.Encrypt(Ticket);
                //create a new authentication cookie - and set its expiration date
                var AuthenticationCookie = new HttpCookie(FormsAuthentication.FormsCookieName, EncryptedTicket)
                                               {
                                                   Expires = Ticket.Expiration,
                                                   HttpOnly = true,
                                                   Secure = FormsAuthentication.RequireSSL
                                               };


                Current.Response.Cookies.Add(AuthenticationCookie);

Answer 1

Why go to all that effort when a simple keep-alive on the client page will keep the forms authentication cookie alive?

jQuery example:

$(function() {
    window.setInterval(keepalive, 600000); // run keepalive every 10 mins
});

function keepalive()
{
   $.get({url:'/myemptykeepalivepage.aspx',cache:false});
}

When the client closes the browser, the interval function is cancelled and voila, the forms auth ticket will expire naturally.