Table 1 Authentication classes for user-side entities as illustrated in Figure 2

[ U→P]

User (U) authentication by the service provider (P)

[ U→S]

User (U) authentication by the server system (S)

(commonly called user authentication)

[ C→P]

Client (C) authentication by the service provider (P)

[ C→S]

Client (C) authentication by the server system (S)