Propagate a base URI that is based upon the uri from the request

So if a user makes a request to `http://my.hostname/...` instead of `http://localhost:8900`, all the URIs returned by the auth API use `http://my.hostname/...`

That base URI should also get propagated to all the plugins, so they can generate correct URIs if necessary.
While that was probably an invalid `obj` tag since it wasn't actually a qualified name, this type of docstring might make it a bit harder to find the implementation...