A specification for IdP hinting

This document defines a generic browser-based protocol for conveying - to services - hints about the IdPs or SP-IdP-proxies that should be used for authenticating the principal. This protocol, colloquially referred to as Identity Provider (IdP) hinting, can greatly simplify the discovery process for the end-user, by enabling entities to produce and send hints that can be consumed by SP-IdP-proxies for routing the user to the correct upstream SP-IdP-Proxy or authenticating IdP.