Characterization of web single sign-on protocols

Single Sign On (SSO) protocols are today integrated in millions of web services so end users can authenticate to a third-party identity provider (IdP) to access multiple services. IdPs normally provide integration tools that hide almost all implementation details and allow developers to implement SSO in minutes. Such integration tools along with cumbersome protocol specifications result in developers without a clear view of the underlying SSO protocol. This article presents a conceptual characterization of web SSO protocols through their assertions and their features that help preserve the privacy of the user resources involved in SSO.