now we want to use our own domain (shared.jovo.to), so we CNAME shared.jovo.to to shared.jovo.to.s3.amazonaws.com. and put http://shared.jovo.to into the Setting "Web URL"
The http URL now is http://shared.jovo.to/my-file.jpg (fine!)
but the https URL is https://shared.jovo.to.s3.amazonaws.com/my-file.jpg
which kind of works, but gives a security warning, because serving files from S3 with own SSL certificate is not possible and so the domain and the default AES S3 certificate do not match.
Nothing much Cyberduck can do about this.