The Shibboleth System is a standards based, open source software package for web single sign-on across or within organizational boundaries. It allows sites to make informed authorization decisions for individual access of protected online resources in a privacy-preserving manner.
This library determines current_user from environment variables set by mod_shib in Apache. An interface to login as any user is also provided for running in development.
rack-shibboleth - nascent Rack-based implementation that works with Nginx and other non-Apache servers