In search for a User, Group, Role & Security Java Library

I've been longing for a Java library that would cover all the needs of authorization and authentication within an application in a sensible manner. The library shouldn't require huge EJB structures and should allow being used within a POJO context.

I've searched and found three useful libraries:

1. Apache Ki http://incubator.apache.org/ki/

2. java.security http://java.sun.com/javase/technologies/security/

3. Spring Security http://www.acegisecurity.org/

The one that drives my curiosity the most is Apache Ki. Seems very promising.