WebSessionSecurityContextRepository changes session id

Fixes: gh-4842

web/src/main/java/org/springframework/security/web/server/context/WebSessionServerSecurityContextRepository.java

@@ -38,7 +38,7 @@ public class WebSessionServerSecurityContextRepository
 					session.getAttributes().put(SESSION_ATTR, context);
 				}
 			})
-			.then();
+			.flatMap(session -> session.changeSessionId());
 	}
 
 	public Mono<SecurityContext> load(ServerWebExchange exchange) {

web/src/test/java/org/springframework/security/web/server/context/WebSessionServerSecurityContextRepositoryTests.java

@@ -0,0 +1,67 @@
+/*
+ * 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.server.context;
+
+import org.junit.Test;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.security.core.context.SecurityContext;
+import org.springframework.security.core.context.SecurityContextImpl;
+import org.springframework.web.server.WebSession;
+
+import static org.assertj.core.api.Assertions.*;
+
+/**
+ * @author Rob Winch
+ * @since 5.0
+ */
+public class WebSessionServerSecurityContextRepositoryTests {
+
+	private MockServerWebExchange exchange = MockServerWebExchange.from(
+		MockServerHttpRequest.get("/"));
+
+	private WebSessionServerSecurityContextRepository repository = new WebSessionServerSecurityContextRepository();
+
+	@Test
+	public void saveAndLoadWhenDefaultsThenFound() {
+		SecurityContext expected = new SecurityContextImpl();
+		this.repository.save(this.exchange, new SecurityContextImpl()).block();
+
+		SecurityContext actual = this.repository.load(this.exchange).block();
+
+		assertThat(actual).isEqualTo(expected);
+	}
+
+	@Test
+	public void saveAndLoadWhenNullThenDeletes() {
+		SecurityContext context = new SecurityContextImpl();
+		this.repository.save(this.exchange, new SecurityContextImpl()).block();
+		this.repository.save(this.exchange, null).block();
+
+		SecurityContext actual = this.repository.load(this.exchange).block();
+
+		assertThat(actual).isNull();
+	}
+
+	@Test
+	public void saveWhenNewContextThenChangeSessionId() {
+		String originalSessionId = this.exchange.getSession().block().getId();
+		this.repository.save(this.exchange, new SecurityContextImpl()).block();
+		WebSession session = this.exchange.getSession().block();
+		assertThat(session.getId()).isNotEqualTo(originalSessionId);
+	}
+}