Support for SMART v2

SMART Backend Services - https://chat.fhir.org/#narrow/stream/179170-smart/topic/SMART.20Backend.20Services.20and.20SMART.20App.20Launch/near/241417920

Launch context (e.g. patient) in the introspection response - https://chat.fhir.org/#narrow/stream/179170-smart/topic/ONC.20preamble.20-.20security.20issue.20for.20token.20introspection.3F/near/241413072

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