This document specifies mechanisms for cross-domain password-based authenticated key exchange, all of which are four-party password-based authenticated key exchange (4PAKE) protocols. Such protocols let two communicating entities establish a shared session key using just the login passwords that they share with their respective domain authentication servers. The authentication servers, assumed to be part of a standard public key infrastructure (PKI), act as ephemeral certification authorities (CAs) that certify key materials that the users can subsequently use to exchange and agree on as a session key.
This document does not specify the means to be used to establish a shared password between an entity and its corresponding domain server. This document also does not define the implementation of a PKI and the means for two distinct domain servers to exchange or verify their respective public key certificates.