Hi Rob,
I don't think session time-out will work here, as closing the browser is not the normal flow when you do a log in.
Then, consider the PC OS freezing and user has to reboot. That is like closing abruptly the browser.
Closing the browser without log in out is not a normal event or processing. And I need to clean what ever data is in the file for that session or user after a non-normal session closing.
If its there no way to clean files when the user does not log out and simply close the browse, then garbage will stay for ever in the file.
Hector