You hand out a token, often a json web token, to an authenticated user, which is then validated for each request. A token is basically a hall pass which is signed by your central authority. Depending on how “instant” removal of users needs to be, you sync with a central identity provider each time or you rely on short lived tokens.

What instance should I chose?

You can choose any you want that’s the beauty of the fediverse!

Instance shuts down and I have to register with an new one…

What the fuck is wrong with people?

Did he state he was arrested? Title just says cuffed.

Markets are not rational, simply because humans are not rational. The pipeline could have been blocked at any time in the last two years.