Timee, Inc. NAT Consulting LLC YAuth.JP LLC This specification defines a new response mode for RFC6749 that uses HTML5 Web Messaging (a.k.a window.postMessage()) instead of the redirect for the Authorization Response from the Authorization Endpoint. It defines two modes: simple mode and relay mode. Relay mode can be used to protect the access token in the implicit grant case by confining it within the origins of authorization server or resource server and preventing it from being read by the client.