Typically, a user proves to the system who they are by entering a valid user name and a valid password. Authorization is the process of identifying what a user can do. For example, after logging in to a system, a user may try to issue commands. The authorization function determines whether the user is permitted to issue those commands. In some systems, authorization and authentication are merged into a single process.
Accounting is the process of measuring the resources a user has consumed.
Typically, accounting measures the amount of system time a user has used, or the amount of data a user has sent and received. Authentication, or the identification of an individual wishing to use a computer service, is a key component of information technology infrastructure. Heretofore, authorization for services has been an implication of authentication, since these functions were both performed and managed together at the local level by the service itself. However, as more services requiring access control have proliferated, this older model has led to a concomitant proliferation of logon IDs and passwords such that a typical active user of several network services must acquire and remember several different logon identities. Newer models for access control separate authentication from authorization, allowing a single means of verifying the identity of a potential user of a service.