Kerberos is a trusted third party network authentication protocol, initially developed as a part of MIT's Project Athena. Kerberos was designed to provide exceptionally strong authentication using secret key cryptography. However, interestingly, with Kerberos v5, the user's password is never sent across the network, not even in encrypted form, except during administration. Kerberos is usually used to implement a single sign-on solution, wherein users authenticate themselves just once to access information on any of several systems.
You can make use of Kerberos under JDK 1.4. Here, JAAS is used for authentication and authorization and Java Generic Security Service (GSS) API is used to establish a secure context for communication with a peer application. For details, see the paper Single Sign-on Using Kerberos in Java.