CsrfWebFilter places Mono<CsrfToken>

Fixes: gh-4855

samples/javaconfig/webflux-form/src/main/java/sample/CsrfControllerAdvice.java

@@ -0,0 +1,38 @@
+/*
+ * 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 sample;
+
+import org.springframework.security.web.server.csrf.CsrfToken;
+import org.springframework.web.bind.annotation.ControllerAdvice;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.server.ServerWebExchange;
+import reactor.core.publisher.Mono;
+
+import static org.springframework.security.web.reactive.result.view.CsrfRequestDataValueProcessor.DEFAULT_CSRF_ATTR_NAME;
+
+/**
+ * @author Rob Winch
+ * @since 5.0
+ */
+@ControllerAdvice
+public class CsrfControllerAdvice {
+	@ModelAttribute
+	public Mono<CsrfToken> csrfToken(ServerWebExchange exchange) {
+		Mono<CsrfToken> csrfToken = exchange.getAttribute(CsrfToken.class.getName());
+		return csrfToken.doOnSuccess(token -> exchange.getAttributes().put(DEFAULT_CSRF_ATTR_NAME, token));
+	}
+}