Absolutely, within a 'closed' environment (e.g. where you have control over your walled garden, what Apps are installed or offered to users, etc), you can do all sorts of cool and clever things with custom interfaces, APIs, and auto- or assisted- logins. This is true today for Hotspot operators (within their own garden and App, they can do anything they want, more or less). This is also true for roaming aggregators (they use their own APIs accessed through the walled garden of Hotspots in their network). None of these solutions require IETF or any standards... I think it is a mistake to try and figure out a common API for everyone to use, as it will never fit all use-cases. In my opinion, we can only create sort of 'core' protocols to convey configuration and network feedback and let the industry decide how it applies to their use-cases.