Add CsrfServerLogoutHandler

Create a CsrfServerLogoutHandler which invalidates the current CsrfToken

Fixes gh-4840

web/src/main/java/org/springframework/security/web/server/csrf/CsrfServerLogoutHandler.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2002-2018 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.security.web.server.csrf;
+
+import org.springframework.security.core.Authentication;
+import org.springframework.security.web.server.WebFilterExchange;
+import org.springframework.security.web.server.authentication.logout.ServerLogoutHandler;
+import org.springframework.util.Assert;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * {@link CsrfServerLogoutHandler} is in charge of removing the {@link CsrfToken} upon logout. A
+ * new {@link CsrfToken} will then be generated by the framework upon the next request.
+ *
+ * @author Eric Deandrea
+ * @since 5.1
+ */
+public class CsrfServerLogoutHandler implements ServerLogoutHandler {
+	private final ServerCsrfTokenRepository csrfTokenRepository;
+
+	/**
+	 * Creates a new instance
+	 * @param csrfTokenRepository The {@link ServerCsrfTokenRepository} to use
+	 */
+	public CsrfServerLogoutHandler(ServerCsrfTokenRepository csrfTokenRepository) {
+		Assert.notNull(csrfTokenRepository, "csrfTokenRepository cannot be null");
+		this.csrfTokenRepository = csrfTokenRepository;
+	}
+
+	/**
+	 * Clears the {@link CsrfToken}
+	 *
+	 * @param exchange the exchange
+	 * @param authentication the {@link Authentication}
+	 * @return A completion notification (success or error)
+	 */
+	@Override
+	public Mono<Void> logout(WebFilterExchange exchange, Authentication authentication) {
+		return this.csrfTokenRepository.saveToken(exchange.getExchange(), null);
+	}
+}