So my intention is to have a login in my iOS app that allows for either our standard email/pwd registration, or login with Facebook. We are also creating rest services to get a
Have you looked at the iOS docs for Single Sign On (SSO)? https://developers.facebook.com/docs/guides/mobile/#ios
You can share an app ID across mobile, canvas and web site and the same user auth works for each environment.
Check out: https://developers.facebook.com/docs/authentication/
Facebook Platform provides a number of ways to use the above OAuth flows in different app types, including Websites, Apps on Facebook.com, Mobile and Desktop Apps.
Design for Facebook authentication in an iOS app that also accesses a secured web service
This post helped me undesrtand it more. If I am not mistaken, the flow goes like this:
Let me know if I am missing anything.
You just need to insert users Facebook key to your database to know if its authenticated with Facebook. Use OAuth at ios side authenticate user take users secret key send it to your rest web-service and save it with users other info.