OptionalextraExtra corresponds to the user.Info.GetExtra() method from the authenticator. Since that is input to the authorizer it needs a reflection here.
OptionalgroupsGroups is the groups you're testing for.
OptionalnonNonResourceAttributes describes information for a non-resource access request
OptionalresourceResourceAuthorizationAttributes describes information for a resource access request
OptionaluidUID information about the requesting user.
OptionaluserUser is the user you're testing for. If you specify "User" but not "Groups", then is it interpreted as "What if User were not a member of any groups
SubjectAccessReviewSpec is a description of the access request. Exactly one of ResourceAuthorizationAttributes and NonResourceAuthorizationAttributes must be set