Ask HN: How can I invite facebook friends to join my application via api?

Hi guys, I'm very confused about this.<p>I want to implement a system that allows users to invite their friends from facebook to join my external application (which is not a facebook application). They could either send an email to the whole list, or send a message.<p>I'm really frustrated because I can't find how to do this via api. Also I'm not sure if I should use facebook connect or what (why don't they have oauth?). I'm trying to do it with ruby on rails by the way.<p>Any kind of help would be appreciated.