Radiance has a specific interface for authentication. Currently only one standard implementation is offered for this, called r-simple-auth, which uses a password scheme to authenticate users. r-simple-auth should be loaded automatically when you depend on the auth interface in your application.

If you are looking for authorization instead, that is handled through the user interface and the check, grant, etc. functions. Again, a standard implementation is offered for this interface, so you should be able to just start using it.