Mastodon implementation misses the point
Grant requires to provide keys and the instance to log in to at initialization. This is not how Mastodon, or pretty much any federated social network works. The fundamental rule of Mastodon is, there's no single instance of it, anyone can set up their own instance, and communicate flawlessly with people from other instances. Per [Mastodon docs](https://docs.joinmastodon.org/client/guidelines/#login): "_The user must be able to login to any Mastodon server from the app. This means you must ask for the server's domain and use the app registrations API to [dynamically obtain OAuth2 credentials](https://docs.joinmastodon.org/methods/apps/)._". The box is ticked on provider list, but the implementation is just nonsense.