OptionalchallengeThe WWW-Authenticate challenge of a 401 when no credential came (Bearer).
OptionalopenapiIts security schemes for OpenAPIFeature's spec: alternatives, each the
schemes presented together. The gates of web-kit set it; a gate of
your own may ([[{ name: 'mtls', scheme: { type: 'mutualTLS' } }]]).
Proves who made a request: returns the actor,
nullwhen the request does not carry this gate's credential (another gate may take it), or throws a 401AuthErrorwhen it carries one that is not valid.