What is AAA?
As far as VPNs are concerned, AAA stands for Authentication, Authorization, and Accounting. Those three functions are the key to intelligently controlling access, enforcing policies, auditing usage, and providing the information necessary to do billing for services available on the Internet. Authentication is the process of determining who the user is. It can take the form of assuring that data has come from its claimed source, or of corroborating the claimed identity of a communicating party. Authorization is the process of enforcing policies – of determining what types or qualities of activities, resources, or services a user is permitted. Usually, authorization is in the context of authentication; once you have authenticated a user, they may be authorized different types of access or activity. Accounting is the tracking of which services are used, by whom, when, and for how long.
