All of the following are identity federation standards commonly found in use today except ____________.

WS-Federation is an identity federation standard primarily used in Microsoft environments and enterprise applications, enabling single sign-on across organizational boundaries.

OpenID (specifically OpenID Connect) is an identity layer built on top of the OAuth 2.0 protocol, allowing clients to verify the identity of an end-user based on the authentication performed by an authorization server.

OAuth (Open Authorization) is an open standard for access delegation, commonly used as a way for Internet users to grant websites or applications access to their information on other websites without giving them their passwords. It is often combined with OpenID Connect for identity federation.

PGP (Pretty Good Privacy) is a cryptographic protocol used for encrypting and decrypting data, primarily for email and file encryption, and for creating digital signatures. It is not an identity federation standard used for establishing trust relationships between different identity providers and service providers.