Shibboleth is standards-based, open source middleware software which
provides Web Single SignOn (SSO) 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 software is a C++ implementation of the Service Provider version 2
component of the Shibboleth can be used in Apache Web servers.  The
service provider manages secured resources. User access to resources
is based on assertions received by the service provider (SP) from
an identity provider.

WWW: http://shibboleth.internet2.edu/