Add Reactive Clear-Site-Data Support

1. A new implementation of ServerHttpHeadersWriter has been created to
   add Clear-Site-Data header support.
2. A new implementation of ServerLogoutHandler has been created which
   can be configured to write response headers during logout.
3. Added unit tests for both implementations.

Fixes gh-6743

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

@@ -0,0 +1,55 @@
+/*
+ * 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.web.server.authentication.logout;
+
+import org.springframework.security.core.Authentication;
+import org.springframework.security.web.server.WebFilterExchange;
+import org.springframework.security.web.server.header.ServerHttpHeadersWriter;
+import org.springframework.web.server.ServerWebExchange;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+/**
+ * @author MD Sayem Ahmed
+ * @since 5.2
+ */
+public class HeaderWriterServerLogoutHandlerTests {
+
+	@Test
+	public void constructorWhenHeadersWriterIsNullThenExceptionThrown() {
+		assertThatExceptionOfType(IllegalArgumentException.class)
+				.isThrownBy(() -> new HeaderWriterServerLogoutHandler(null));
+	}
+
+	@Test
+	public void logoutWhenInvokedThenWritesResponseHeaders() {
+		ServerHttpHeadersWriter headersWriter = mock(ServerHttpHeadersWriter.class);
+		HeaderWriterServerLogoutHandler handler = new HeaderWriterServerLogoutHandler(headersWriter);
+		ServerWebExchange serverWebExchange = mock(ServerWebExchange.class);
+		WebFilterExchange filterExchange = mock(WebFilterExchange.class);
+		when(filterExchange.getExchange()).thenReturn(serverWebExchange);
+		Authentication authentication = mock(Authentication.class);
+
+		handler.logout(filterExchange, authentication);
+
+		verify(headersWriter).writeHttpHeaders(serverWebExchange);
+	}
+}

web/src/test/java/org/springframework/security/web/server/header/ClearSiteDataServerHttpHeadersWriterTests.java

@@ -0,0 +1,120 @@
+/*
+ * 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.web.server.header;
+
+import org.springframework.http.server.reactive.ServerHttpResponse;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.security.web.server.header.ClearSiteDataServerHttpHeadersWriter.Directive;
+import org.springframework.util.CollectionUtils;
+import org.springframework.web.server.ServerWebExchange;
+
+import org.assertj.core.api.AbstractAssert;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+/**
+ * @author MD Sayem Ahmed
+ * @since 5.2
+ */
+public class ClearSiteDataServerHttpHeadersWriterTests {
+
+	@Test
+	public void constructorWhenMissingDirectivesThenThrowsException() {
+		assertThatExceptionOfType(IllegalArgumentException.class)
+				.isThrownBy(ClearSiteDataServerHttpHeadersWriter::new);
+	}
+
+	@Test
+	public void writeHttpHeadersWhenSecureConnectionThenHeaderWritten() {
+		ClearSiteDataServerHttpHeadersWriter writer = new ClearSiteDataServerHttpHeadersWriter(Directive.ALL);
+		ServerWebExchange secureExchange = MockServerWebExchange.from(
+				MockServerHttpRequest.get("https://localhost")
+						.build());
+
+		writer.writeHttpHeaders(secureExchange);
+
+		assertThat(secureExchange.getResponse()).hasClearSiteDataHeaderDirectives(Directive.ALL);
+	}
+
+	@Test
+	public void writeHttpHeadersWhenInsecureConnectionThenHeaderNotWritten() {
+		ClearSiteDataServerHttpHeadersWriter writer = new ClearSiteDataServerHttpHeadersWriter(Directive.ALL);
+		ServerWebExchange insecureExchange = MockServerWebExchange.from(
+				MockServerHttpRequest.get("/")
+						.build());
+
+		writer.writeHttpHeaders(insecureExchange);
+
+		assertThat(insecureExchange.getResponse()).doesNotHaveClearSiteDataHeaderSet();
+	}
+
+	@Test
+	public void writeHttpHeadersWhenMultipleDirectivesSpecifiedThenHeaderContainsAll() {
+		ClearSiteDataServerHttpHeadersWriter writer = new ClearSiteDataServerHttpHeadersWriter(
+				Directive.CACHE, Directive.COOKIES);
+		ServerWebExchange secureExchange = MockServerWebExchange.from(
+				MockServerHttpRequest.get("https://localhost")
+						.build());
+
+		writer.writeHttpHeaders(secureExchange);
+
+		assertThat(secureExchange.getResponse()).hasClearSiteDataHeaderDirectives(Directive.CACHE, Directive.COOKIES);
+	}
+
+	private static ClearSiteDataAssert assertThat(ServerHttpResponse response) {
+		return new ClearSiteDataAssert(response);
+	}
+
+	private static class ClearSiteDataAssert extends AbstractAssert<ClearSiteDataAssert, ServerHttpResponse> {
+
+		ClearSiteDataAssert(ServerHttpResponse response) {
+			super(response, ClearSiteDataAssert.class);
+		}
+
+		void hasClearSiteDataHeaderDirectives(Directive... directives) {
+			isNotNull();
+			List<String> header = getHeader();
+			String actualHeaderValue = String.join("", header);
+			String expectedHeaderVale = Stream.of(directives)
+					.map(Directive::getHeaderValue)
+					.collect(Collectors.joining(", "));
+			if (!actualHeaderValue.equals(expectedHeaderVale)) {
+				failWithMessage("Expected to have %s as Clear-Site-Data header value but found %s",
+						expectedHeaderVale, actualHeaderValue);
+			}
+		}
+
+		void doesNotHaveClearSiteDataHeaderSet() {
+			isNotNull();
+			List<String> header = getHeader();
+			if (!CollectionUtils.isEmpty(header)) {
+				failWithMessage("Expected not to have Clear-Site-Data header set but found %s",
+						String.join("", header));
+			}
+		}
+
+		List<String> getHeader() {
+			return actual.getHeaders()
+					.get(ClearSiteDataServerHttpHeadersWriter.CLEAR_SITE_DATA_HEADER);
+		}
+	}
+}