CORS support in HTTP header predicate

This commit introduces CORS support for the HeadersPredicate in
WebMvc.fn and WebFlux.fn.

Closes gh-24564

Author: poutsma

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RequestPredicates.java

@@ -550,7 +550,12 @@ public HeadersPredicate(Predicate<ServerRequest.Headers> headersPredicate) {
 
 		@Override
 		public boolean test(ServerRequest request) {
-			return this.headersPredicate.test(request.headers());
+			if (CorsUtils.isPreFlightRequest(request.exchange().getRequest())) {
+				return true;
+			}
+			else {
+				return this.headersPredicate.test(request.headers());
+			}
 		}
 
 		@Override

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/RequestPredicatesTests.java

@@ -198,6 +198,18 @@ public void headers() {
 		assertThat(predicate.test(request)).isFalse();
 	}
 
+	@Test
+	public void headersCors() {
+		RequestPredicate predicate = RequestPredicates.headers(headers -> false);
+		MockServerHttpRequest mockRequest = MockServerHttpRequest.options("https://example.com")
+				.header("Origin", "https://example.com")
+				.header(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, "PUT")
+				.build();
+		ServerRequest request = new DefaultServerRequest(MockServerWebExchange.from(mockRequest), Collections.emptyList());
+		assertThat(predicate.test(request)).isTrue();
+	}
+
+
 	@Test
 	public void contentType() {
 		MediaType json = MediaType.APPLICATION_JSON;

spring-webmvc/src/main/java/org/springframework/web/servlet/function/RequestPredicates.java

@@ -543,7 +543,12 @@ public HeadersPredicate(Predicate<ServerRequest.Headers> headersPredicate) {
 
 		@Override
 		public boolean test(ServerRequest request) {
-			return this.headersPredicate.test(request.headers());
+			if (CorsUtils.isPreFlightRequest(request.servletRequest())) {
+				return true;
+			}
+			else {
+				return this.headersPredicate.test(request.headers());
+			}
 		}
 
 		@Override

spring-webmvc/src/test/java/org/springframework/web/servlet/function/RequestPredicatesTests.java

@@ -197,6 +197,16 @@ public void headers() {
 		assertThat(predicate.test(request)).isFalse();
 	}
 
+	@Test
+	public void headersCors() {
+		RequestPredicate predicate = RequestPredicates.headers(headers -> false);
+		MockHttpServletRequest servletRequest = new MockHttpServletRequest("OPTIONS", "https://example.com");
+		servletRequest.addHeader("Origin", "https://example.com");
+		servletRequest.addHeader(HttpHeaders.ACCESS_CONTROL_REQUEST_METHOD, "PUT");
+		ServerRequest request = new DefaultServerRequest(servletRequest, emptyList());
+		assertThat(predicate.test(request)).isTrue();
+	}
+
 	@Test
 	public void contentType() {
 		MediaType json = MediaType.APPLICATION_JSON;