Java security technology originally focused on creating a safe environment in which to run potentially untrusted code downloaded from the public network.
With the latest release of the java platform, fine grained access controls can be placed upon critical ressources with regard to the identity of the running applets and applications, which are distinguished by where the code came from and who signed it.
However, the java platform still lacks the means to enforce access controls based on the identity of the user who runs the code.
Java Authentification and Authorization Service (JAAS), a framework and programming
Interface that augments the java platform with both user-based authentication and access control capabilities.

Authentification of users, to reliably and securely detremine who is currently executing Java code.
Authorization of users, to ensure they have the access control rights required to do the actions performed.