misskey and micro.blog from @manton both support client registration for clients like this by simply providing a website url
it's called "indieauth" (displayed in the login info row, otherwise falls back to mastodon-style app-creation-based registration)
there is a newer emerging standard for dynamic client registration, but no one supports it yet - I'll add it when one does!
micro.blog doesn't support C2S follows via the outbox yet, but we can fallback to the micro.blog api here
you'll notice that browser.pub not only requests the ability to follow, but _also_ to read, generally
this gives the logged-in user the ability to explore ActivityPub collections that may not be public, only accessible via auth (if the server supports such collections over ActivityPub C2S)
in theory, you could imagine building a thing on top of these collections that looks like your personal mastodon timeline, but using spec-standard ActivityPub
in practice, tho, here is my mastodon inbox 🤦♂️