B2 documentation suggests that after adding a CNAME (eg. cdn.ente.io) for their bucket endpoint (eg. bucket.s3.eu-central-003.backblazeb2.com), you will be able to replace the latter with the former. This breaks with the native B2 APIs with the following error:

```

{

  "code": "not_found",

  "message": "/api/top_level_url_mapping",

  "status": 404

}

```

The last I checked was a few months ago, not sure if things have been fixed now.

With Workers, we simply fetch the remote resource from B2 and return it back to the client, acting as a thin proxy.