Need Advice: Best way to join Mem Provider w/ 3rd party Authentication

Hello,
I'm starting to develop a website that will have two options for logging in:
1.  Log in using Facebook Connect
OR

2.  Have local account at this site using Sql Membership Provider.


I'm thinking there are several ways of developing this.
1.  Create custom Membership Provider that works with both SqlMembershipProvider AND Facebook Connect.  The idea is that I could handle two different types of sessions/accounts by using an ambiguous custom membership provider.
Pros/Logic

If Facebook user:  know user by FB user ID.If Membership user: know user by Membership GUID.
Cons: 
Difficult to code custom membership provider.Custom Membership provider would be bug prone.

2.  Base all membership operations from SqlMembershipProvider.  When user logs in with facebook, (if new: create mem user an ...