Add DelegatingServerLogoutHandler(List<ServerLogoutHandler> delegates)

Issue: gh-4839

web/src/main/java/org/springframework/security/web/server/authentication/logout/DelegatingServerLogoutHandler.java

@@ -16,6 +16,7 @@
 
 package org.springframework.security.web.server.authentication.logout;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.stream.Collectors;
@@ -41,6 +42,11 @@ public class DelegatingServerLogoutHandler implements ServerLogoutHandler {
 		this.delegates = Arrays.asList(delegates);
 	}
 
+	public DelegatingServerLogoutHandler(List<ServerLogoutHandler> delegates) {
+		Assert.notEmpty(delegates, "delegates cannot be null or empty");
+		this.delegates = new ArrayList<>(delegates);
+	}
+
 	@Override
 	public Mono<Void> logout(WebFilterExchange exchange, Authentication authentication) {
 		Stream<Mono<Void>> results = this.delegates.stream().map(delegate -> delegate.logout(exchange, authentication));

web/src/test/java/org/springframework/security/web/server/authentication/logout/DelegatingServerLogoutHandlerTests.java

@@ -30,6 +30,8 @@ import org.springframework.security.web.server.WebFilterExchange;
 
 import reactor.test.publisher.PublisherProbe;
 
+import java.util.List;
+
 /**
  * @author Eric Deandrea
  * @since 5.1
@@ -57,13 +59,21 @@ public class DelegatingServerLogoutHandlerTests {
 	}
 
 	@Test
-	public void constructorWhenNullThenIllegalArgumentException() {
+	public void constructorWhenNullVargsThenIllegalArgumentException() {
 		assertThatThrownBy(() -> new DelegatingServerLogoutHandler((ServerLogoutHandler[]) null))
 				.isExactlyInstanceOf(IllegalArgumentException.class)
 				.hasMessage("delegates cannot be null or empty")
 				.hasNoCause();
 	}
 
+	@Test
+	public void constructorWhenNullListThenIllegalArgumentException() {
+		assertThatThrownBy(() -> new DelegatingServerLogoutHandler((List<ServerLogoutHandler>) null))
+				.isExactlyInstanceOf(IllegalArgumentException.class)
+				.hasMessage("delegates cannot be null or empty")
+				.hasNoCause();
+	}
+
 	@Test
 	public void constructorWhenEmptyThenIllegalArgumentException() {
 		assertThatThrownBy(() -> new DelegatingServerLogoutHandler(new ServerLogoutHandler[0]))