it seems that this method doesn't work for logging out the user from an app on facebook, i dont want to log the user from facebook itself like with getLogoutUrl, only from the app.
if the user uncheck the email field on the dialogue box the first time he log in with facebook, he needs to logout from the app, in order to log in again without unchecking the email field, so he have a second chance of signing in to my site.
this method doesn't work anymore:i'm on php SDK V4
setcookie('fbs_455857397897935','', time()-100);
// kill the session session_destroy();
455857397897935 is the app id