Add SpringTestContext.addFilter

Add SpringTestContext.addFilter which allows Spring Security's tests
to specify a Filter to be added to the SpringTestContext.

Closes gh-12071

config/src/test/java/org/springframework/security/config/annotation/web/builders/HttpSecurityDeferAddFilterTest.java

@@ -46,7 +46,7 @@ import org.springframework.security.web.header.HeaderWriterFilter;
 import static org.assertj.core.api.Assertions.assertThat;
 
 @ExtendWith(SpringTestContextExtension.class)
-public class HttpSecurityAddFilterTest {
+public class HttpSecurityDeferAddFilterTest {
 
 	public final SpringTestContext spring = new SpringTestContext(this);
 

config/src/test/java/org/springframework/security/config/test/SpringTestContext.java

@@ -57,6 +57,8 @@ public class SpringTestContext implements Closeable {
 
 	private List<Filter> filters = new ArrayList<>();
 
+	private DeferAddFilter deferAddFilter = new DeferAddFilter();
+
 	private List<Consumer<ConfigurableWebApplicationContext>> postProcessors = new ArrayList<>();
 
 	public SpringTestContext(Object test) {
@@ -113,16 +115,17 @@ public class SpringTestContext implements Closeable {
 	}
 
 	public SpringTestContext mockMvcAfterSpringSecurityOk() {
-		return addFilter(new OncePerRequestFilter() {
+		this.deferAddFilter.addFilter(new OncePerRequestFilter() {
 			@Override
 			protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
 					FilterChain filterChain) {
 				response.setStatus(HttpServletResponse.SC_OK);
 			}
 		});
+		return this;
 	}
 
-	private SpringTestContext addFilter(Filter filter) {
+	public SpringTestContext addFilter(Filter filter) {
 		this.filters.add(filter);
 		return this;
 	}
@@ -145,9 +148,10 @@ public class SpringTestContext implements Closeable {
 		this.context.refresh();
 		if (this.context.containsBean(BeanIds.SPRING_SECURITY_FILTER_CHAIN)) {
 			// @formatter:off
-			MockMvc mockMvc = MockMvcBuilders.webAppContextSetup(this.context).
-					apply(springSecurity())
-					.apply(new AddFilter())
+			MockMvc mockMvc = MockMvcBuilders.webAppContextSetup(this.context)
+					.addFilters(this.filters.toArray(new Filter[0]))
+					.apply(springSecurity())
+					.apply(this.deferAddFilter)
 					.build();
 			// @formatter:on
 			this.context.getBeanFactory().registerResolvableDependency(MockMvc.class, mockMvc);
@@ -157,12 +161,18 @@ public class SpringTestContext implements Closeable {
 		bpp.processInjection(this.test);
 	}
 
-	private class AddFilter implements MockMvcConfigurer {
+	private static class DeferAddFilter implements MockMvcConfigurer {
+
+		private List<Filter> filters = new ArrayList<>();
+
+		void addFilter(Filter filter) {
+			this.filters.add(filter);
+		}
 
 		@Override
 		public RequestPostProcessor beforeMockMvcCreated(ConfigurableMockMvcBuilder<?> builder,
 				WebApplicationContext context) {
-			builder.addFilters(SpringTestContext.this.filters.toArray(new Filter[0]));
+			builder.addFilters(this.filters.toArray(new Filter[0]));
 			return null;
 		}