[tracking] OpenId-based Auth flows

[gnunicorn]

Thanks to Olli's work we know have an openID / MAS available on M2 to test/develop against.

Reminder, what we want to achieve (eventually) is implement the flows described in the 'Enagaging Onboarding' balsamiq, which is already designed with the OpenID flows in mind.

Overall flow

1. For the development, we want to keep the existing flows in place, and with a development-enven-flag enable the new flows to be built in its place instead.
2. we then, over several weeks, want to build out and develop the features mentioned guarded by that enven flag
3. Once we have a complete implementation, we will schedule to convert the live server to also provide MAS support and from there, we will start shipping a version of Acter with the new feature turned on

specific tasks listed below as sub-items