The Spring Security plugins are built on the
Spring Security project which provides a flexible, extensible framework for building all sorts of authentication and authorization schemes. The plugins are modular so you can install just the functionality that you need for your application. There is a Core plugin which supports form-based authentication, encrypted/salted passwords, HTTP Basic authentication, etc. and secondary dependent plugins provide alternate functionality such as OpenID authentication, ACL support, etc.
See the
plugin page for basic information and the
user guide for detailed information.