Update @MessageMapping to match input/output cardinality

Author: eleftherias

config/src/test/java/org/springframework/security/config/annotation/rsocket/RSocketMessageHandlerITests.java

@@ -185,19 +185,6 @@ public void retrieveFluxWhenDataStringAndSecureThenDenied() throws Exception {
 		assertThat(this.controller.payloads).isEmpty();
 	}
 
-	@Test
-	public void retrieveFluxWhenDataStringAndPublicThenGranted() throws Exception {
-		String data = "a";
-		List<String> hi = this.requester.route("retrieve-flux")
-				.data(data)
-				.retrieveFlux(String.class)
-				.collectList()
-				.block();
-
-		assertThat(hi).contains("hello a");
-		assertThat(this.controller.payloads).containsOnly(data);
-	}
-
 	@Test
 	public void sendWhenSecureThenDenied() throws Exception {
 		String data = "hi";
@@ -287,7 +274,7 @@ Flux<String> retrieveFlux(Flux<String> payload) {
 		}
 
 		@MessageMapping({"secure.send", "send"})
-		Mono<Void> send(Flux<String> payload) {
+		Mono<Void> send(Mono<String> payload) {
 			return payload
 					.doOnNext(this::add)
 					.then(Mono.fromRunnable(() -> {