I've got a Facebook iframe application that is completely external. By this I mean that once a user accesses the canvas URL to load the application, all the links in the iframe app go to my servers, and the canvas page never gets refreshed unless the user navigates to somewhere else on Facebook and comes back (or does a browser refresh).

On the initial load of the app where Facebook creates the iframe, I get passed all the usual parameters like fb_sig_user which allows me to create an internal app session based on the facebook user. This app session (which is not the Facebook session, it's my own app session) is all I need to allow the user to work with the app.

The problem comes an hour later. If the user leaves the computer, or uses the app for more than an hour, the Facebook session expires. There are some app pages which require fetching friend information, and once the FB session has expired, these pages break, throwing out errors such as "Error: Session key invalid or no longer valid".

My question is whether there is a way to refresh the user's Facebook session from within an iframe application to keep it from expiring an hour later. Do any of the API calls do this? Is there a Facebook Connect trick to ping something? Is there any definitive method to keep it alive? I haven't been able to find any examples that specifically address this.