Add MockServerConfigurer to WebTestClient

Issue: SPR-15674

spring-test/src/main/java/org/springframework/test/web/reactive/server/AbstractMockServerSpec.java

@@ -35,6 +35,8 @@ abstract class AbstractMockServerSpec<B extends WebTestClient.MockServerSpec<B>>
 
 	private final List<WebFilter> filters = new ArrayList<>(4);
 
+	private final List<MockServerConfigurer> configurers = new ArrayList<>(4);
+
 
 	@Override
 	public <T extends B> T webFilter(WebFilter... filter) {
@@ -42,20 +44,23 @@ abstract class AbstractMockServerSpec<B extends WebTestClient.MockServerSpec<B>>
 		return self();
 	}
 
+	@Override
+	public <T extends B> T apply(MockServerConfigurer configurer) {
+		configurer.afterConfigureAdded(this);
+		this.configurers.add(configurer);
+		return self();
+	}
+
 	@SuppressWarnings("unchecked")
 	private <T extends B> T self() {
 		return (T) this;
 	}
 
-
 	@Override
 	public WebTestClient.Builder configureClient() {
 		WebHttpHandlerBuilder builder = initHttpHandlerBuilder();
-		builder.filters(currentFilters -> {
-			List<WebFilter> toPrepend = new ArrayList<>(this.filters);
-			Collections.reverse(toPrepend);
-			toPrepend.forEach(filter -> currentFilters.add(0, filter));
-		});
+		builder.filters(theFilters -> theFilters.addAll(0, this.filters));
+		this.configurers.forEach(configurer -> configurer.beforeServerCreated(builder));
 		return new DefaultWebTestClientBuilder(builder.build());
 	}
 
@@ -65,7 +70,6 @@ abstract class AbstractMockServerSpec<B extends WebTestClient.MockServerSpec<B>>
 	 */
 	protected abstract WebHttpHandlerBuilder initHttpHandlerBuilder();
 
-
 	@Override
 	public WebTestClient build() {
 		return configureClient().build();

spring-test/src/main/java/org/springframework/test/web/reactive/server/MockServerConfigurer.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2002-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.test.web.reactive.server;
+
+import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
+
+/**
+ * Contract that frameworks or applications can use to pre-package a set of
+ * customizations to a {@link WebTestClient.MockServerSpec} and expose that
+ * as a shortcut.
+ *
+ * <p>An implementation of this interface can be plugged in via
+ * {@link WebTestClient.MockServerSpec#apply} where instances are likely obtained
+ * via static methods, e.g.:
+ *
+ * <pre class="code">
+ * import static org.example.ExampleSetup.securitySetup;
+ *
+ * // ...
+ *
+ * WebTestClient.bindToController(new TestController())
+ *     .apply(securitySetup("foo","bar"))
+ *     .build();
+ * </pre>
+ *
+ * @author Rossen Stoyanchev
+ * @since 5.0
+ */
+public interface MockServerConfigurer {
+
+	/**
+	 * Invoked immediately, i.e. before this method returns.
+	 * @param serverSpec the serverSpec to which the configurer is added
+	 */
+	default void afterConfigureAdded(WebTestClient.MockServerSpec<?> serverSpec) {
+	}
+
+	/**
+	 * Invoked just before the mock server is built. Use this hook to inspect
+	 * and/or modify application-declared filtes and exception handlers,
+	 * @param builder the builder for the {@code HttpHandler} that will handle
+	 * requests (i.e. the mock server)
+	 */
+	default void beforeServerCreated(WebHttpHandlerBuilder builder) {
+	}
+
+}

spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java

@@ -203,6 +203,12 @@ public interface WebTestClient {
 		 */
 		<T extends B> T webFilter(WebFilter... filter);
 
+		/**
+		 * Shortcut for pre-packaged customizations to the mock server setup.
+		 * @param configurer the configurer to apply
+		 */
+		<T extends B> T apply(MockServerConfigurer configurer);
+
 		/**
 		 * Proceed to configure and build the test client.
 		 */