This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
public interface ReactiveOpaqueTokenIntrospector
A contract for introspecting and verifying an OAuth 2.0 token.
A typical implementation of this interface will make a request to an
OAuth 2.0 Introspection Endpoint
to verify the token and return its attributes, indicating a successful verification.
Another sensible implementation of this interface would be to query a backing store
of tokens, for example a distributed cache.