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.
Is this really "`unicode`"? `base_uri_from_request` says it returns `str` and that's where the value comes from.