the login handler is processed when you click the "submit" button in the login form. Once the user is connected ('logged in') the handler is not processed any more until the user logs out.
hth!
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Xavier Serna
eZ Publish Certified Developer
Departament de Software
Microblau S.L. - http://www.microblau.net
+34 937 466 205
On siteaccess where you Require login (the setting in site.ini used by admin siteaccess by default), it will call the checkUser() function on your login handler on every page request. But it will also not allow non logged in users to access the site, so not the best match for facebook login.
As mention in the forum on facebook_connect project page, sso handler is probably a better match, it is only executed on each request if user is not logged in. Such a handler exist in the svn version of facebook_connect that has received a lot of changes.