core/src/main/java/org/springframework/security/core/context/ReactiveSecurityContextHolder.java
public static Mono<SecurityContext> getContext() {
		return Mono.subscriberContext()
			.filter( c -> c.hasKey(SECURITY_CONTEXT_KEY))
			.flatMap( c-> c.<Mono<SecurityContext>>get(SECURITY_CONTEXT_KEY));
	}
public static Mono<SecurityContext> getContext() {
		return Mono.subscriberContext()
			.filter( c -> c.hasKey(SECURITY_CONTEXT_KEY))
			.flatMap( c-> c.<Mono<SecurityContext>>get(SECURITY_CONTEXT_KEY));
	}
Gets the {@code Mono<SecurityContext>} from Reactor {@link Context}
@return the {@code Mono<SecurityContext>}