asp.net cookies, authentication and session timeouts

I have an asp.net website that uses forms authentication. There are a few things I keep in sessions like username, userID, email, etc.

I allow the user to stay logged into the website by setting a long expiration date on the authentication cookie. So it's very common for the session to expire while the user is still authenticated.

The problem I am running into is that sometimes the user's session times out but they're still authenticated. So for example, one of my user pages (which requires authentication) will say "Welcome Mike" when their session is active but once it expires it will say "Welcome [blank]" because the info is no longer in the session, yet they are still authenticated.

What's the best way to handle this? Should I resync the session info when the info is no longer there? Or should I move the user info (username, userID, email) into cookies and not worry about session timeouts?

I do not want to set the session length to something like 60 minutes or more. What i want is for my users to be able to login once and not worry about having to login again until they explicitly logout.

Avoid using session as much as you can, if you can get away without seesion it makes multi-server deployments qutie a bit easier. Probably, Name and email are easy candidates for cookies. It's easy to fake a cookie, so userID may not be a good idea depending on your security needs.

The forms authentication cookies are encrypted and you can add extra data to those cookies (See details below). It's probably hackable but not nearly as easily as a simple cookie.

Here is the code I have used in the past slightly modified to remove some project specific details. Call this in the LoggedIn event of the login control.

void AddUserIDToAuthCookie(string userID)  
{  
  //There is no way to directly set the userdata portion of a FormAuthenticationTicket  
  //without re-writing the login portion of the Login control  
  //  
  //I find it easier to pull the cookie that the Login control inserted out  
  //and create a new cookie with the userdata set  

  HttpCookie authCookie = Response.Cookies[AUTH_COOKIE];
  if(authCookie == null)
  {
    return;
  }

  Response.Cookies.Remove(AUTH_COOKIE);

  FormsAuthenticationTicket oldTicket = FormsAuthentication.Decrypt(authCookie.Value);
  var newTicket =
    new FormsAuthenticationTicket(oldTicket.Version, oldTicket.Name, oldTicket.IssueDate, oldTicket.Expiration,
                                  oldTicket.IsPersistent, userID, oldTicket.CookiePath);

  authCookie.Value = FormsAuthentication.Encrypt(newTicket);

  Response.Cookies.Add(authCookie);
}

FYI, I copied this from an old project and edited it here to remove some project specific bits, so it may not compile, but it'll be very close.

To get the ID in your webpage...

FormsAuthenticationTicket ticket = ((FormsIdentity) Page.User.Identity).Ticket;
string id = ticket.UserData;

I used this mechanism to store an id that was not part of the aspnetdb user data. If all your identity data is handled by the aspnetdb, you may only need to access the Page.User.Identity object.

Personally, I would keep the 20 minute default and add a "keep alive" functionality to your site. Make a simple javascript that polls, say heartbeat.aspx, every 5 minutes to keep the session alive. This will extend the session and authentication without keeping crazy authentication tokens.

There are a few examples (bad in my opinion) of how to do this. I ended up using something based on AjaxLines's session timeout prevention. Instead of using the ajax library, though, I simply used an xhtml request directly. Nothing is really needed more than a timed javascript call to a GET on the heartbeat page.