What are the dangers of tying one Facebook UID to multiple application accounts / tokens?

I'm getting started with a mix of Facebook Registration and Facebook Connect and wondering if there's a problem with my existing users foo@bar.com and bar@foo.com both connecting their accounts on my site to the same Facebook UID.

I can guess that if foo@bar.com connects to Facebook through my application, then bar@foo.com might have to re-authenticate because my application would use a different token for the same Facebook UID the second time. Would Facebook somehow reject the use of multiple tokens from my application?

To be clear - I know I can control whether or not the un开发者_如何学Ciqueness is a problem in my database, I'm mostly trying to anticipate how Facebook will treat multiple different requests from the same application and if there might be any problems in how the application behaves.

Your question is so fogy. What you actually want to do? When you want to connect with facebook, it means you allow users to login in your system with their facebook accounts. So authentication will be done at facebook end. I am unable to understand your double ID phenomenon. What do you mean by two different ID's?