With an app password in `TCM_ATPROTO_APP_PASSWORD`, a sign-in needs no browser and covers any scope; it's kept with the password, so later sign-ins, for any scope and with no password given, need nothing, and when its tokens are gone it signs in again by itself. A wrong password is refused, and nothing kept.
Kept sign-ins are read only from the user's own file: not a link (refused), and not one others can read (made private); they're written without following a link left in the way.