feature: Add failure handler for cookie verification

This feature allows to customize the behaviour of what should be done in
case the cookie could not be verified.

By default the cookie is silently ignored, as before.

Closes #1

pom.xml

@@ -96,6 +96,11 @@
         <artifactId>assertj-core</artifactId>
         <version>3.10.0</version>
       </dependency>
+      <dependency>
+        <groupId>org.mockito</groupId>
+        <artifactId>mockito-core</artifactId>
+        <version>2.19.0</version>
+      </dependency>
       <dependency>
         <groupId>com.fasterxml.jackson</groupId>
         <artifactId>jackson-bom</artifactId>
@@ -145,6 +150,11 @@
       <artifactId>junit-jupiter-engine</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-test</artifactId>

src/main/java/com/innoq/spring/cookie/flash/CookieFlashMapManager.java

@@ -16,6 +16,7 @@
 package com.innoq.spring.cookie.flash;
 
 import com.innoq.spring.cookie.flash.codec.FlashMapListCodec;
+import com.innoq.spring.cookie.flash.verification.CookieVerificationFailureHandler;
 import com.innoq.spring.cookie.security.CookieValueSigner;
 import org.springframework.util.Assert;
 import org.springframework.web.servlet.FlashMap;
@@ -37,6 +38,8 @@ public final class CookieFlashMapManager extends AbstractFlashMapManager {
     private final FlashMapListCodec codec;
     private final CookieValueSigner signer;
     private final String cookieName;
+    private CookieVerificationFailureHandler verificationFailureHandler =
+        CookieVerificationFailureHandler.ignoreFailures();
 
     public CookieFlashMapManager(FlashMapListCodec codec,
             CookieValueSigner signer) {
@@ -53,6 +56,12 @@ public CookieFlashMapManager(FlashMapListCodec codec,
         this.cookieName = cookieName;
     }
 
+    public void setVerificationFailureHandler(
+            CookieVerificationFailureHandler verificationFailureHandler) {
+        Assert.notNull(verificationFailureHandler, "CookieVerificationFailureHandler must not be null");
+        this.verificationFailureHandler = verificationFailureHandler;
+    }
+
     @Override
     protected List<FlashMap> retrieveFlashMaps(HttpServletRequest request) {
         final Cookie cookie = getCookie(request, cookieName);
@@ -88,16 +97,14 @@ protected Object getFlashMapsMutex(HttpServletRequest request) {
     private List<FlashMap> decode(String value) {
         final String[] signatureAndPayload = reverse(value).split("--", 2);
         if (signatureAndPayload.length != 2) {
-            // TODO logging
-            return null;
+            return verificationFailureHandler.onInvalidValue(value);
         }
 
         final String signature = reverse(signatureAndPayload[0]);
         final String payload = reverse(signatureAndPayload[1]);
 
         if (!isVerified(payload, signature)) {
-            // TODO logging
-            return null;
+            return verificationFailureHandler.onInvalidSignature(payload, signature);
         }
 
         return codec.decode(payload);

src/main/java/com/innoq/spring/cookie/flash/verification/CookieVerificationFailureHandler.java

@@ -0,0 +1,31 @@
+/**
+ * Copyright 2018 innoQ Deutschland GmbH
+ *
+ * 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 com.innoq.spring.cookie.flash.verification;
+
+import org.springframework.web.servlet.FlashMap;
+
+import java.util.List;
+
+public interface CookieVerificationFailureHandler {
+
+    List<FlashMap> onInvalidValue(String value);
+
+    List<FlashMap> onInvalidSignature(String payload, String signature);
+
+    static CookieVerificationFailureHandler ignoreFailures() {
+        return IgnoreCookieVerificationFailureHandler.INSTANCE;
+    }
+}

src/main/java/com/innoq/spring/cookie/flash/verification/IgnoreCookieVerificationFailureHandler.java

@@ -0,0 +1,35 @@
+/**
+ * Copyright 2018 innoQ Deutschland GmbH
+ *
+ * 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 com.innoq.spring.cookie.flash.verification;
+
+import org.springframework.web.servlet.FlashMap;
+
+import java.util.List;
+
+enum IgnoreCookieVerificationFailureHandler
+        implements CookieVerificationFailureHandler {
+    INSTANCE;
+
+    @Override
+    public List<FlashMap> onInvalidValue(String value) {
+        return null;
+    }
+
+    @Override
+    public List<FlashMap> onInvalidSignature(String payload, String signature) {
+        return null;
+    }
+}

src/test/java/com/innoq/spring/cookie/flash/CookieFlashMapManagerTest.java

@@ -16,6 +16,7 @@
 package com.innoq.spring.cookie.flash;
 
 import com.innoq.spring.cookie.flash.codec.jackson.JacksonFlashMapListCodec;
+import com.innoq.spring.cookie.flash.verification.CookieVerificationFailureHandler;
 import com.innoq.spring.cookie.security.CookieValueSigner;
 import org.junit.jupiter.api.Test;
 import org.springframework.mock.web.MockHttpServletRequest;
@@ -30,6 +31,9 @@
 import static java.util.Collections.emptyList;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.entry;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
 
 class CookieFlashMapManagerTest {
 
@@ -65,6 +69,43 @@ void retrieveFlashMaps_withValidCookie_returnsFlashMaps() {
         assertThat(flashMap.getTargetRequestPath()).isEqualTo("/foo");
     }
 
+    @Test
+    void retrieveFlashMaps_withInvalidCookieValue_callsGivenVerificationFailureHandlerAndUsesItsReturnValue() {
+        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/");
+        request.setCookies(new Cookie("flash", "ABCDEF"));
+
+        CookieVerificationFailureHandler verificationFailureHandler =
+            mock(CookieVerificationFailureHandler.class);
+        when(verificationFailureHandler.onInvalidValue("ABCDEF")).thenReturn(null);
+
+        sut.setVerificationFailureHandler(verificationFailureHandler);
+
+        List<FlashMap> flashMaps = sut.retrieveFlashMaps(request);
+
+        assertThat(flashMaps).isNull();
+        verify(verificationFailureHandler).onInvalidValue("ABCDEF");
+    }
+
+    @Test
+    void retrieveFlashMaps_withInvalidCookieValueSignatur_callsGivenVerificationFailureHandlerAndUsesItsReturnValue() {
+        String cookieValue = "abcd--efgh";
+
+        MockHttpServletRequest request = new MockHttpServletRequest("GET", "/");
+        request.setCookies(new Cookie("flash", cookieValue));
+
+        CookieVerificationFailureHandler verificationFailureHandler =
+            mock(CookieVerificationFailureHandler.class);
+        when(verificationFailureHandler.onInvalidSignature("abcd", "efgh"))
+            .thenReturn(null);
+
+        sut.setVerificationFailureHandler(verificationFailureHandler);
+
+        List<FlashMap> flashMaps = sut.retrieveFlashMaps(request);
+
+        assertThat(flashMaps).isNull();
+        verify(verificationFailureHandler).onInvalidSignature("abcd", "efgh");
+    }
+
     @Test
     void updateFlashMaps_withSingleFlashMap_writesCookie() {
         MockHttpServletRequest request = new MockHttpServletRequest("GET", "/");