Want to assign usernames & passwords in C#

In our MVC 4 app, I would like to assign usernames (generated from user's first & last name) and passwords (generated from last four of user's ssn).
1) Should I place my code in the controller?  (that is where the user enters the form data which will be used to create the username/password)
2) Can I use the existing Simple Membership to take advantage of its builtin features? (would like to add Role functionality)