Business Application Template will give you an ASP.NET project, there with a Services folder and three new files: AuthenticationService, UserInformation, UserRegistrationService. These are all services to expose authentication and membership integration. Running the template by default will give you a new “login” link in the upper right and clicking on that implements a new ChildWindow for login:
Notice the "Register now” link which then uses another ChildWindow control for registration:
Registering a new user uses the UserRegistrationService to add a new user to the system. If you look at the UserRegistrationService you’ll see that it uses the ASP.NET Membership APIs.