Polish XFrameOptionsHeaderWriter

Issue: gh-4559

web/src/main/java/org/springframework/security/web/header/writers/frameoptions/XFrameOptionsHeaderWriter.java

@@ -82,8 +82,10 @@ public final class XFrameOptionsHeaderWriter implements HeaderWriter {
 	 */
 	public void writeHeaders(HttpServletRequest request, HttpServletResponse response) {
 		if (XFrameOptionsMode.ALLOW_FROM.equals(frameOptionsMode)) {
-			String allowFromValue = allowFromStrategy.getAllowFromValue(request);
-			if (allowFromValue != null && !allowFromValue.equals(XFrameOptionsMode.DENY.getMode())) {
+			String allowFromValue = this.allowFromStrategy.getAllowFromValue(request);
+			if(XFrameOptionsMode.DENY.getMode().equals(allowFromValue)) {
+				response.setHeader(XFRAME_OPTIONS_HEADER, XFrameOptionsMode.DENY.getMode());
+			} else if (allowFromValue != null) {
 				response.setHeader(XFRAME_OPTIONS_HEADER,
 						XFrameOptionsMode.ALLOW_FROM.getMode() + " " + allowFromValue);
 			}

web/src/test/java/org/springframework/security/web/header/writers/frameoptions/XFrameOptionsHeaderWriterTests.java

@@ -0,0 +1,46 @@
+/*
+ * 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 org.springframework.security.web.header.writers.frameoptions;
+
+import org.junit.Test;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+
+import java.util.Arrays;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Rob Winch
+ * @since 5.0
+ */
+public class XFrameOptionsHeaderWriterTests {
+	private MockHttpServletRequest request = new MockHttpServletRequest();
+	private MockHttpServletResponse response = new MockHttpServletResponse();
+
+	@Test
+	public void writeHeadersWhenWhiteList() {
+		WhiteListedAllowFromStrategy whitelist = new WhiteListedAllowFromStrategy(Arrays.asList("example.com"));
+		XFrameOptionsHeaderWriter writer = new XFrameOptionsHeaderWriter(whitelist);
+
+
+		writer.writeHeaders(this.request, this.response);
+
+		assertThat(this.response.getHeaderValue(XFrameOptionsHeaderWriter.XFRAME_OPTIONS_HEADER)).isEqualTo("DENY");
+	}
+
+}