Allow Global CORS configuration to be disable (#2779)

Property: spring.cloud.gateway.globalcors.enabled

Reason: CORS filter was applied automatically and it doens't allow developers to customise CORS for specific scenarios. Disabling SCG listener allows developers to customise or reuse CORS logic.

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@@ -268,6 +268,7 @@ public class GatewayAutoConfiguration {
 	}
 
 	@Bean
+	@ConditionalOnProperty(name = "spring.cloud.gateway.globalcors.enabled", matchIfMissing = true)
 	public CorsGatewayFilterApplicationListener corsGatewayFilterApplicationListener(
 			GlobalCorsProperties globalCorsProperties, RoutePredicateHandlerMapping routePredicateHandlerMapping,
 			RouteDefinitionLocator routeDefinitionLocator) {

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/cors/CorsGlobalTests.java

@@ -19,11 +19,14 @@ package org.springframework.cloud.gateway.cors;
 import java.util.Arrays;
 
 import org.junit.jupiter.api.Test;
+import org.junit.runner.RunWith;
 import reactor.core.publisher.Mono;
 
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.SpringBootConfiguration;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.cloud.gateway.filter.cors.CorsGatewayFilterApplicationListener;
 import org.springframework.cloud.gateway.test.BaseWebClientTests;
 import org.springframework.context.annotation.Import;
 import org.springframework.http.HttpHeaders;
@@ -32,6 +35,7 @@ import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.web.reactive.function.client.ClientResponse;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -76,4 +80,18 @@ public class CorsGlobalTests extends BaseWebClientTests {
 
 	}
 
+	@RunWith(SpringRunner.class)
+	@SpringBootTest(classes = TestConfig.class, properties = "spring.cloud.gateway.globalcors.enabled=false")
+	public static class DisabledByProperty {
+
+		@Autowired(required = false)
+		private CorsGatewayFilterApplicationListener listener;
+
+		@org.junit.Test
+		public void corsGatewayFilterApplicationListenerIsMissing() {
+			assertThat(listener).isNull();
+		}
+
+	}
+
 }