none: a public client that identifies itself with client_id only and
presents no secret (e.g. a PKCE flow, or a grant for which
requireClientAuthentication is disabled).
This adapter only resolves the client. Whether a secret-less client is
acceptable for the request is a policy decision owned by the orchestrator
(it knows the grant type, the requireClientAuthentication config and
whether this is a PKCE request).
Kind: global class
Extends: AbstractClientAuthentication
See: https://datatracker.ietf.org/doc/html/rfc6749#section-2.1