Add CsrfServerLogoutHandler

Create a CsrfServerLogoutHandler which invalidates the current CsrfToken

Fixes gh-4840

web/src/test/java/org/springframework/security/web/server/csrf/CsrfServerLogoutHandlerTests.java

@@ -0,0 +1,62 @@
+package org.springframework.security.web.server.csrf;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.mockito.Mockito.*;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.security.authentication.TestingAuthenticationToken;
+import org.springframework.security.web.server.WebFilterExchange;
+import org.springframework.web.server.WebFilterChain;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * @author Eric Deandrea
+ * @since 5.1
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class CsrfServerLogoutHandlerTests {
+	@Mock
+	private ServerCsrfTokenRepository csrfTokenRepository;
+
+	@Mock
+	private WebFilterChain filterChain;
+
+	private MockServerWebExchange exchange;
+
+	private WebFilterExchange filterExchange;
+
+	private CsrfServerLogoutHandler handler;
+
+	@Before
+	public void setup() {
+		this.exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/").build());
+		this.filterExchange = new WebFilterExchange(this.exchange, this.filterChain);
+		this.handler = new CsrfServerLogoutHandler(this.csrfTokenRepository);
+		when(this.csrfTokenRepository.saveToken(this.exchange, null)).thenReturn(Mono.empty());
+	}
+
+	@Test
+	public void constructorNullCsrfTokenRepository() {
+		assertThatExceptionOfType(IllegalArgumentException.class)
+				.isThrownBy(() -> new CsrfServerLogoutHandler(null))
+				.withMessage("csrfTokenRepository cannot be null")
+				.withNoCause();
+	}
+
+	@Test
+	public void logoutRemovesCsrfToken() {
+		this.handler.logout(
+				this.filterExchange,
+				new TestingAuthenticationToken("user", "password", "ROLE_USER")).block();
+
+		verify(this.csrfTokenRepository).saveToken(this.exchange, null);
+	}
+}