Returns the URL to send the user to.
Once the user returns to the app and presses some button,
run finishAuthorizeDesktop, await it, and (optimally)
use the returned LastFMAuthorized instead.
Perform a "read" operation on the Last.fm api. This is typically done to
get information about artists, albums, or tracks, or when authenticated to
get information about the user or their listening habits.