I am currently doing this on my website. However, keep in mind that the membership provider does not align correctly with FB Authentication. In my project, I have 2 controllers for FB authentication, and the other for forms authentication. The forms authentication code is pretty much the standard code introduced in the new project, except that I encrypt my password with BCrypt after adding the Salt value.
Please refer to my blog http://theocdcoder.com/tutorial-integrating-facebook-authentication-asp-net-mvc-3/ for FB integration. The reason I did not include another form code is because it is independent of the FB code.
Also, in the FB login method in the controller, you will have to process the script if the user has already registered through the Forms method, if then not create a new record for him.
Hope this helps.
Ketan source share