From Facebook Developer Wiki

Gack! Why didn't you use javascript?

How do I delete cookies? Standard practice is to set a cookie with the same name that has an expiration time in the past, but this doesn't work. Also, how do I overwrite cookies?

Setting a cookie to a past time-stamp does not appear to work presently. You can however set it to one second in the future to have it expire extremely soon. --502041253 09:17, 18 March 2009 (PDT)

What's the expiration time of session cookies on FB gateway ? In the case of standard workflow, the session cookie (who implicitly has an expiration time and so not expire after 24 hours) expire when we close the browser. But here, it seems that the expiration time is much more than 24 hours. It causes me some problem with sticky sessions on my application, since once a user came on a server, he still goes on the same and he's never balanced, even if the idle server session time is over, because of the session cookie who's still alive.

Are you setting an "expires" attribute to a time greater than 24 hours? If not, please file a bug. Thanks, Pete (563683308 11:32, 8 April 2009 (PDT))

No, the expiration time of a session cookie depends on the client, in most of cases the browser which expires the cookie when it closes. So I don't set any expiration time. Here, the client is the FB gateway. I'll post the bug.