I'll reconsider using SASL instead. I have the HTTPS-transport version
almost ready, so for now I'll go with that, to have a working
solution. There's still some other questions, mostly related to how
the data should be stored on the receiver, so I want to get it out for
people to test. The underlying transport is an implementation detail,
mostly visible in the way that authentication is done, so a new
transport can be added, and the old one deprecated or even removed.