My client has asked me to create an application in which user can either register and sign in by filling form or just by using facebook connect. A user is using (facebook username) to sign in in my site. Now again this user tries to register himself by filling form using this same email address. Now what the application must do? 1. Allow user to have seperate accounts in website 1) as facebook user 2) as normal registered user with same email address 2. Disallow user to create account with the same email he/she is using in facebook 3. Please suggest any third option