This is part of the work to improve how @hollo does OAuth and to bring it up to par with Mastodon 4.3

However, one of those next steps requires a rather major refactor of how we do authorization grants and access tokens. Before we make those changes it would be great to be able to have some baseline test coverage in place.

Related issues:
- https://github.com/fedify-dev/hollo/issues/125
- https://github.com/fedify-dev/hollo/issues/49
- https://github.com/fedify-dev/hollo/issues/44
- https://github.com/fedify-dev/hollo/issues/14