Tonight I'll be adding support for this in an app (Poppy.fm) that already supports both Last.fm and ListenBrainz. Apologies if I missed this, but am I understanding correctly that users must get a Rocksky API key? (In other words, there's no OAuth support for native iOS users who'll expect a "Sign in with Bluesky"-type flow?)

OAuth is possible, but the tricky part is not really the auth flow, it's the client-side ATProto write logic. To scrobble properly, the client needs to keep enough historical scrobble state to avoid duplicates, and Rocksky doesn't only publish a scrobble record. It may also need to publish related records like artist, album, and track metadata. So I'd like to make the integration easier, but it needs a bit more than "just OAuth".