Checkpoint is both a Ruby library and an abstract model for authorizing user activity within an application.
It takes its name from the concept of a physical security checkpoint, where someone (or some device) verifies identity and credentials before granting access to some space or resource. This documentation covers a range of topics related to authentication and authorization, primarily focused on how to implement secure, understandable, and maintainable business rules in web applications built in Ruby. It comes out of the University of Michigan Library, where enterprise, legacy, and new systems must all interoperate.
Checkpoint emphasizes the use of policies and object-oriented design, giving examples from very simple rules through complex group- and role-based scenarios.
Checkpoint does not handle authentication at all. See Keycard for a library that does so and provides identity attributes that can be used as the basis for grants and policies.