Learning about Authentication and Security Issues

The more common distributed architecture consists of client and distributed / centralized server the following three approaches to security can be envisioned in this environment. To assure user identity we have to rely on each workstation and to enforce a security policy based on user ID we have to rely on each server.
By trusting that the client system concerning the identity of its user each client system authenticates themselves to server. The client has to prove his/her identity to invoke a service as well as the servers also invoke a service as well as the server also has to prove their identity to client