The Exact Editions platform now uses the Shibboleth system for federated sign-on to web services. The system is Open Source and much used in the British academic universe, amongst others. Here is a video from JISC explaining some of the advantages (warning: the vides is a little bit ‘corporate’).
Federated services are always a good idea on the web? Such shared technologies all depend on trust….which is becoming ever more important in the web as services are layered on top of each other.