Kerberos /ˈkərbərəs/ is a computer network authentication protocol which works on the basis of 'tickets' to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner.
is the act of confirming the truth of an attribute of a single piece of data claimed true by an entity.
is the function of specifying access rights to resources related to information security and computer security in general and to access control in particular.
Authentication is about who somebody is.
Authorisation is about what they're allowed to do.
TGS: Ticket Granting Service