I'm a bit wary of logging in. Does Spotify provide OAuth with fine-grained control, i.e. will the page only get access to the music history or could it in theory change playlists and billing information?
Yes. When you click auth you can see the permissive it asks for. Which is profile and history.
It looks like they request these permissions: user-top-read, playlist-read-private, playlist-read-collaborative and they also gets your your name, username and profile picture.
Seems a neat way to collect information for their startup. Maybe a Spotify competitor, or a datamarket for selling people's music preferences.
The Pudding is, per the footer on that page, "a digital publication that explains ideas debated in culture with visual essays". It's been around for a few years already. https://pudding.cool/archives/