The Pluggable Authentication Service (PAS) is an alternative to the standard Zope User Folder or the popular Group User Folder (GRUF). PAS has a highly modular design, which is very powerful, but also a lot harder to understand.
PAS is built around the concepts of interfaces and plugins: all possible tasks related to user and group management and authentication are described in separate interfaces. These interfaces are implemented by plugins which can be selectively enabled per interface.
Plone uses PlonePAS, which extends PAS with a couple of extra plugin types and which adds GRUF compatibility. Since PlonePAS extensions are rarely needed and are subject to change in new Plone releases, this tutorial will focus only on pure PAS features.