Are you saying that you want to have two domains, both pointing to the same bucket, and you want different permissions to apply depending on which domain name was used to access the resource? If so, I don't think we have that functionality. Moreover, we don't currently allow multiple CNAME aliases to point to the same bucket. There was a
recent conversation about this topic on the discussion group.
If you can describe your use case (send it to gs-team AT
google.com and please don't share any proprietary information in your use case description), I'd be happy to write an internal feature request.