How can reactive programming be enabled for key-cache?

[dwang2]

I have developed a reactive security service to retrieve the current user's name using the code snippet provided below. How can I formulate a key-cache expression to asynchronously fetch the username

@service
public class SecurityService {

public Mono<String> username() {
	return ReactiveSecurityContextHolder.getContext()
			.map(securityContext -> {
				Authentication authentication = securityContext.getAuthentication();
				return authentication != null ? authentication.getName() : null;
			});
}

}

[MarcGiffing]

This essential requirements is not supported yet. See #289.