@Nick Wall, You can run a "keep alive" function every five or so minutes that retrieves a page to keep the session alive. The keep alive page should return the logged in user. If the user is "Anonymous", then re-login the user. The page should not require authentication so that it can return Anonymous if the user is no longer logged in.
I'd change the onclick event to an onsubmit event for the form.
<form onsubmit="DEXT.Session.Authenticate(this.form); return false;"...
@Nick Wall, You can run a "keep alive" function every five or so minutes that retrieves a page to keep the session alive. The keep alive page should return the logged in user. If the user is "Anonymous", then re-login the user. The page should not require authentication so that it can return Anonymous if the user is no longer logged in.