Music.
MusicBrainz API is a free Music API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Details from musicbrainz.org.

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Music
The MusicBrainz API is provided by MusicBrainz (musicbrainz.org).
Yes. The MusicBrainz API is listed in the Music category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The MusicBrainz API requires no authentication, so you can start making requests without signing up.
CORS support for the MusicBrainz API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The MusicBrainz API is served over HTTPS, so it's safe to use in production.