Introduce LogoutSuccessEvent

LogoutSuccessEvent is a simple AbstractAuthenticationEvent implementation which indicates successful logout.

By default, LogoutConfigurer will add a new LogoutHandler called LogoutSuccessEventPublishingLogoutHandler to publish this event.

This PR will also fix ConcurrentSessionFilter's composite logoutHandler, now will get LogoutHandler instances from LogoutConfigurer for consistency.

Fixes gh-2900

core/src/main/java/org/springframework/security/authentication/event/LogoutSuccessEvent.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2002-2019 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
+ *
+ *      https://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.security.authentication.event;
+
+import org.springframework.security.core.Authentication;
+
+/**
+ * Application event which indicates successful logout
+ *
+ * @author Onur Kagan Ozcan
+ * @since 5.2.0
+ */
+public class LogoutSuccessEvent extends AbstractAuthenticationEvent {
+
+	public LogoutSuccessEvent(Authentication authentication) {
+		super(authentication);
+	}
+
+}