Code review comment for lp:~cjwatson/launchpad/librarian-accept-macaroon

Would it be better if the librarian talked to the authserver for this?
I'd avoided that approach because it seemed like unnecessary complexity,
but it could easily be done asynchronously and it would allow preserving
the fine-grained permissions, which I'd really like to find a way to do.
We could do it only for the macaroon auth case, which I expect to
continue being comparatively rare.