Facebook connect situation

Question

My app is using its internal registration system for users to signup and login...

I am now checking out the idea of integrating Facebook Connect into my app but i have come to a situation that i think i need some sort of help...

So users in my app upon registration have to select a username and email address which are unique.

What will happen if a user tries to connect via Facebook and that user already exists? their email for example? or what will happen if that user doesnt have a username? can i show them error messages depending in their situation?

Also if the user doesnt have a username on facebook but has an email address that is not registered in my system do i have to show them a new inputfield for them to type in their username before they can access the website further?

Answer 1

All of these scenarios have been explained in registration flows, specifically

My site uses Facebook and my own Registration