> It's interesting that they implement AWS bucket policies, including all AWS-specific syntax/keys/etc, even "arn": https://docs.hetzner.com/storage/object-storage/faq/s3-crede...

It seems the Hetzner's docs say they use MinIO to expose their S3 managed service. I guess everything will be the same as MinIO upstream features and contigurations

I can only find mentions of the minio client as a way of accessing their S3 service. Their introductory page[0] says "Any data you save in your Bucket is saved in a Ceph cluster.", which suggests they use Ceph's radosgw that offers the S3-compatible API[1].

[0] https://docs.hetzner.com/storage/object-storage/overview#obj... [1] https://docs.ceph.com/en/latest/radosgw/s3/