Authentication
T3 takes care of registration, login, logout, password retrieval, etc.
To check if a user is authenticated
self.logged_in
If the user is logged in
self.person_name
the person id (as in db.t2_person.id==id) is in
self.person_id
and the person email is in
self.person_email
You can also check is the user is an administrator
self.is_admin
For group memberships and group based access control refer to the T2 documentation.