Internet-scale Identity Management is a fascinating topic with many facets. The prevalent solution today duplicates identity information at many, separate places and uses as many different passwords to access and protect them. Users cannot handle the resulting plethora of credentials and weak security is the result. Plenty of technical approaches to remedy the situation exist, but little of them have managed to offer a complete and secure solution. Above all of them floats the keyword Single Sign-On as a seemingly trivial way out of the mess. But a great number of pitfalls prevented the...