Document and implement flows with _openid record at root domain
For the use-case, when all sub-users under one domain hold the same Authority/Agent pair.
Suggestion is to describe process of resolution in the way that:
- first search in _openid.domain.example.com
- if not found search in _openid.example.com
- continue until some matching TXT record found.
Open topic: what to do with ACME in this case? Proposal: in case of such setup challenge process is automatically complete without any DNS manipulation.
Edited by Pawel Kowalik