JAAS includes a sample SolarisLoginModule
and NTLoginModule. There should be an
equivalent LinuxLoginModule now that
the JDK is shipped on Linux.

This would also require a new LinuxPrincipal,
LinuxNumericUserPrincipal, and LinuxNumericGroupPrincipal.

The LinuxModule should go in the com.sun.security.auth.module package.
The Linux principals should go into the com.sun.security.auth package.