Subscriptions: Headers for source stream events aren't propagated to subgraphs

[o0Ignition0o]

STRs:

Configure the router to forward Authorization header to all subgraphs.
Open a subscription with an authorization header.

Expected:
Subsequent subgraph calls propagated by the source stream events contain the Authorization header initially provided by the client.

Actual:
No header is forwarded.

Caveat:
Let's be 100% sure dedup still works as expected.