posted 14 years ago
JAAS is quite involved. Acegi was meant as a replacement for it, especially in the context of Spring-based web applications (although I understand it can be used without Spring). It's not a complete replacement, though, e.g. it can use JAAS authentication modules. I'm not sure if Acegi can be used outside of web apps, though.
Many web apps can get by without using either of these; it depends a lot on your requirements.