This introduces a dedicated API for MAS to consume. Companion PR on the
MAS side: element-hq/matrix-authentication-service#4801
This has a few advantages over the previous admin API:
- it works on workers (this will be documented once we stabilise MSC3861
as a whole)
- it is more efficient because more focused
- it propagates trace contexts from MAS
- it is only accessible to MAS (through the shared secret) and will let
us remove the weird hack that made this token 'admin' with a ghost
'@__oidc_admin:' user
The next MAS version should support it, but will be opt-in. The version
after that should use this new API by default
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Co-authored-by: Eric Eastwood <erice@element.io>