Authentication is the means by which you log in and identify yourself. Authorisation is the means by which a service determines whether an authenticated person should have access to a service.
The major authentication services in the university are EASE and Active Directory. Both are synchronised to use the same password.
There is also a central authorisation service provided by an LDAP directory. This gives information about individuals to services so that they can decide whether someone is authorised to use the service or not.