IS spec doesn't mention that X-Matrix auth is different

[turt2live]

It uses destination_is instead of destination

[jcgruenhage]

It doesn't mention that X-Matrix authentication can be used at all, it only mentions access token authentication. I'd argue that destination_is does not provide any value, because you can already see that we're talking to an identity server based on the path in the request (that's also used in the signed json object).