Comment 6 for bug 1576804

I think you can actually already use it as a metadata, you just can put it on "generic" so you need to include it on all your types.

I'm not sure if oslo.policy rules will work against those fields, we should add some checks I guess. Right now I think we just miss the extraction of X-Domain-Id and its usage in oslo.policy. I'll add that, that should be pretty straight forward.