STS - Necessary Cloud Condition

Here is a concrete example of capabilities in Web services that explain why the cloud != mainframe or client/server. In the cloud we expect to need different identity tokens and protocols whether its SAML (and several versions of this), oauth, Information Cards, Kerberos, and many other ways that identity is conveyed. To get interoperability, a security token server (STS) is used to exchange tokens and cross domains. Because by definition there are so many players and relationships in the cloud, a STS is simply a requirement to transact identity across these domains.