Am I imagining right that you're imagining that the startup process is currently Instance : ____ (add account)
and you're interpreting that to mean Instance : ______ (add a new account) rather than Instance: ______ (Add existing account) (which is what it actually is)? In which case startup should ask [add new account] [add existing account] a) then, if you click existing account give you two more options: i) log in by web interface (as normal) ii) log in here then if you choose (i) it sends you to the web browser (as normal) if you choose (ii) it asks you for a username, then password, then (login) (this should be doable with the mastodon API) b) then, if you click 'new account' walk you through the steps of creating a new account, perhaps offering a list of instances, choose a username / accept TOS, etc etc ... Does that sound right?