[GitHub] [wicket] martin-g commented on a change in pull request #439: Wicket 6786: Add Fetch Metadata support

[GitBox <gi...@apache.org>]

martin-g commented on a change in pull request #439:
URL: https://github.com/apache/wicket/pull/439#discussion_r465064988



##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/FetchMetadataRequestCycleListener.java
##########
@@ -0,0 +1,157 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.wicket.protocol.http;
+
+import static java.util.Arrays.asList;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_DEST_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_MODE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_SITE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.VARY_HEADER;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.wicket.core.request.handler.IPageRequestHandler;
+import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
+import org.apache.wicket.request.IRequestHandler;
+import org.apache.wicket.request.IRequestHandlerDelegate;
+import org.apache.wicket.request.component.IRequestablePage;
+import org.apache.wicket.request.cycle.IRequestCycleListener;
+import org.apache.wicket.request.cycle.RequestCycle;
+import org.apache.wicket.request.http.WebResponse;
+import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;
+import org.apache.wicket.util.string.Strings;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Fetch Metadata Request Cycle Listener is Wicket's implementation of Fetch Metadata.
+ * This adds a layer of protection for modern browsers that prevents Cross-Site Request Forgery
+ * attacks.
+ *
+ * This request listener uses the {@link DefaultResourceIsolationPolicy} by default and can be
+ * customized with additional Resource Isolation Policies.
+ *
+ * This listener can be configured to add exempted URL paths that are intended to be used cross-site.
+ *
+ * Learn more about Fetch Metadata and resource isolation
+ * at <a href="https://web.dev/fetch-metadata/">https://web.dev/fetch-metadata/</a>
+ *
+ * @author Santiago Diaz - saldiaz@google.com
+ * @author Ecenaz Jen Ozmen - ecenazo@google.com
+ */
+public class FetchMetadataRequestCycleListener implements IRequestCycleListener {
+
+  private static final Logger log = LoggerFactory
+      .getLogger(FetchMetadataRequestCycleListener.class);
+  public static final int ERROR_CODE = 403;
+  public static final String ERROR_MESSAGE = "Forbidden";
+
+  private final Set<String> exemptedPaths = new HashSet<>();
+  private final List<ResourceIsolationPolicy> resourceIsolationPolicies = new ArrayList<>();
+
+  FetchMetadataRequestCycleListener(ResourceIsolationPolicy... additionalPolicies) {
+    this.resourceIsolationPolicies.add(new DefaultResourceIsolationPolicy());
+    this.resourceIsolationPolicies.addAll(asList(additionalPolicies));
+  }
+
+  void addExemptedPaths(String... exemptions) {
+    Arrays.stream(exemptions)
+        .filter(e -> !Strings.isEmpty(e))
+        .forEach(exemptedPaths::add);
+  }
+
+  @Override
+  public void onBeginRequest(RequestCycle cycle)
+  {
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    logAtDebug("Processing request to: {}", containerRequest.getPathInfo());
+  }
+
+  @Override
+  public void onRequestHandlerResolved(RequestCycle cycle, IRequestHandler handler)
+  {
+    handler = unwrap(handler);
+    Optional<IPageRequestHandler> pageRequestHandler = getPageRequestHandler(handler);
+    if (pageRequestHandler.isEmpty()) {
+      return;
+    }
+
+    IRequestablePage targetedPage = pageRequestHandler.get().getPage();
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    String pathInfo = containerRequest.getPathInfo();
+    if (exemptedPaths.contains(pathInfo)) {
+      logAtDebug("Allowing request to {} because it matches an exempted path", pathInfo);
+      return;
+    }
+
+    for (ResourceIsolationPolicy resourceIsolationPolicy : resourceIsolationPolicies) {
+      if (!resourceIsolationPolicy.isRequestAllowed(containerRequest, targetedPage)) {
+        logAtDebug(
+            "Isolation policy {} has rejected a request to {}",
+            resourceIsolationPolicy.getClass().getSimpleName(),

Review comment:
       You can use `Classes.simpleName()` here. It handles better anonymous/inner classes

##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/FetchMetadataRequestCycleListener.java
##########
@@ -0,0 +1,157 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.wicket.protocol.http;
+
+import static java.util.Arrays.asList;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_DEST_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_MODE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_SITE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.VARY_HEADER;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.wicket.core.request.handler.IPageRequestHandler;
+import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
+import org.apache.wicket.request.IRequestHandler;
+import org.apache.wicket.request.IRequestHandlerDelegate;
+import org.apache.wicket.request.component.IRequestablePage;
+import org.apache.wicket.request.cycle.IRequestCycleListener;
+import org.apache.wicket.request.cycle.RequestCycle;
+import org.apache.wicket.request.http.WebResponse;
+import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;
+import org.apache.wicket.util.string.Strings;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Fetch Metadata Request Cycle Listener is Wicket's implementation of Fetch Metadata.
+ * This adds a layer of protection for modern browsers that prevents Cross-Site Request Forgery
+ * attacks.
+ *
+ * This request listener uses the {@link DefaultResourceIsolationPolicy} by default and can be
+ * customized with additional Resource Isolation Policies.
+ *
+ * This listener can be configured to add exempted URL paths that are intended to be used cross-site.
+ *
+ * Learn more about Fetch Metadata and resource isolation
+ * at <a href="https://web.dev/fetch-metadata/">https://web.dev/fetch-metadata/</a>
+ *
+ * @author Santiago Diaz - saldiaz@google.com
+ * @author Ecenaz Jen Ozmen - ecenazo@google.com
+ */
+public class FetchMetadataRequestCycleListener implements IRequestCycleListener {
+
+  private static final Logger log = LoggerFactory
+      .getLogger(FetchMetadataRequestCycleListener.class);
+  public static final int ERROR_CODE = 403;
+  public static final String ERROR_MESSAGE = "Forbidden";
+
+  private final Set<String> exemptedPaths = new HashSet<>();
+  private final List<ResourceIsolationPolicy> resourceIsolationPolicies = new ArrayList<>();
+
+  FetchMetadataRequestCycleListener(ResourceIsolationPolicy... additionalPolicies) {
+    this.resourceIsolationPolicies.add(new DefaultResourceIsolationPolicy());
+    this.resourceIsolationPolicies.addAll(asList(additionalPolicies));
+  }
+
+  void addExemptedPaths(String... exemptions) {
+    Arrays.stream(exemptions)
+        .filter(e -> !Strings.isEmpty(e))
+        .forEach(exemptedPaths::add);
+  }
+
+  @Override
+  public void onBeginRequest(RequestCycle cycle)
+  {
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    logAtDebug("Processing request to: {}", containerRequest.getPathInfo());
+  }
+
+  @Override
+  public void onRequestHandlerResolved(RequestCycle cycle, IRequestHandler handler)
+  {
+    handler = unwrap(handler);
+    Optional<IPageRequestHandler> pageRequestHandler = getPageRequestHandler(handler);
+    if (pageRequestHandler.isEmpty()) {
+      return;
+    }
+
+    IRequestablePage targetedPage = pageRequestHandler.get().getPage();
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    String pathInfo = containerRequest.getPathInfo();
+    if (exemptedPaths.contains(pathInfo)) {
+      logAtDebug("Allowing request to {} because it matches an exempted path", pathInfo);
+      return;
+    }
+
+    for (ResourceIsolationPolicy resourceIsolationPolicy : resourceIsolationPolicies) {
+      if (!resourceIsolationPolicy.isRequestAllowed(containerRequest, targetedPage)) {
+        logAtDebug(
+            "Isolation policy {} has rejected a request to {}",
+            resourceIsolationPolicy.getClass().getSimpleName(),
+            pathInfo
+        );
+        throw new AbortWithHttpErrorCodeException(ERROR_CODE, ERROR_MESSAGE);
+      }
+    }
+  }
+
+  @Override
+  public void onEndRequest(RequestCycle cycle)
+  {
+    // set vary headers to avoid caching responses processed by Fetch Metadata
+    // caching these responses may return 403 responses to legitimate requests
+    // or defeat the protection
+    if (cycle.getResponse() instanceof WebResponse)
+    {
+      WebResponse webResponse = (WebResponse)cycle.getResponse();
+      if (webResponse.isHeaderSupported())
+      {
+        webResponse.addHeader(VARY_HEADER, SEC_FETCH_DEST_HEADER + ", "
+            + SEC_FETCH_SITE_HEADER + ", " + SEC_FETCH_MODE_HEADER);
+      }
+    }
+  }
+
+  private static IRequestHandler unwrap(IRequestHandler handler) {
+    while (handler instanceof IRequestHandlerDelegate)

Review comment:
       nit: our code style is to use `{` and `}` even for one-liners

##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/CsrfPreventionRequestCycleListener.java
##########
@@ -110,11 +110,15 @@
  * <li>{@link #onSuppressed(HttpServletRequest, String, IRequestablePage)} when an origin was in
  * conflict and the request should be suppressed</li>
  * </ul>
+ *
+ * @see FetchMetadataRequestCycleListener
+ * @deprecated
  */
-public class CsrfPreventionRequestCycleListener implements IRequestCycleListener
+@Deprecated(since = "XXX")

Review comment:
       "9.1.0"
   But IMO it needs some work before being deprecated. The logic should be extracted in a new class implementing ResourceIsolationPolicy that this listener should extend from. This way we could remove this class for Wicket 10 (as we do with all deprecated classes in a major version release).

##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/FetchMetadataRequestCycleListener.java
##########
@@ -0,0 +1,157 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.wicket.protocol.http;
+
+import static java.util.Arrays.asList;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_DEST_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_MODE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_SITE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.VARY_HEADER;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.wicket.core.request.handler.IPageRequestHandler;
+import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
+import org.apache.wicket.request.IRequestHandler;
+import org.apache.wicket.request.IRequestHandlerDelegate;
+import org.apache.wicket.request.component.IRequestablePage;
+import org.apache.wicket.request.cycle.IRequestCycleListener;
+import org.apache.wicket.request.cycle.RequestCycle;
+import org.apache.wicket.request.http.WebResponse;
+import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;
+import org.apache.wicket.util.string.Strings;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Fetch Metadata Request Cycle Listener is Wicket's implementation of Fetch Metadata.
+ * This adds a layer of protection for modern browsers that prevents Cross-Site Request Forgery
+ * attacks.
+ *
+ * This request listener uses the {@link DefaultResourceIsolationPolicy} by default and can be
+ * customized with additional Resource Isolation Policies.
+ *
+ * This listener can be configured to add exempted URL paths that are intended to be used cross-site.
+ *
+ * Learn more about Fetch Metadata and resource isolation
+ * at <a href="https://web.dev/fetch-metadata/">https://web.dev/fetch-metadata/</a>
+ *
+ * @author Santiago Diaz - saldiaz@google.com
+ * @author Ecenaz Jen Ozmen - ecenazo@google.com
+ */
+public class FetchMetadataRequestCycleListener implements IRequestCycleListener {
+
+  private static final Logger log = LoggerFactory
+      .getLogger(FetchMetadataRequestCycleListener.class);
+  public static final int ERROR_CODE = 403;
+  public static final String ERROR_MESSAGE = "Forbidden";
+
+  private final Set<String> exemptedPaths = new HashSet<>();
+  private final List<ResourceIsolationPolicy> resourceIsolationPolicies = new ArrayList<>();
+
+  FetchMetadataRequestCycleListener(ResourceIsolationPolicy... additionalPolicies) {
+    this.resourceIsolationPolicies.add(new DefaultResourceIsolationPolicy());
+    this.resourceIsolationPolicies.addAll(asList(additionalPolicies));
+  }
+
+  void addExemptedPaths(String... exemptions) {
+    Arrays.stream(exemptions)
+        .filter(e -> !Strings.isEmpty(e))
+        .forEach(exemptedPaths::add);
+  }
+
+  @Override
+  public void onBeginRequest(RequestCycle cycle)
+  {
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    logAtDebug("Processing request to: {}", containerRequest.getPathInfo());
+  }
+
+  @Override
+  public void onRequestHandlerResolved(RequestCycle cycle, IRequestHandler handler)
+  {
+    handler = unwrap(handler);
+    Optional<IPageRequestHandler> pageRequestHandler = getPageRequestHandler(handler);
+    if (pageRequestHandler.isEmpty()) {
+      return;
+    }
+
+    IRequestablePage targetedPage = pageRequestHandler.get().getPage();
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    String pathInfo = containerRequest.getPathInfo();
+    if (exemptedPaths.contains(pathInfo)) {
+      logAtDebug("Allowing request to {} because it matches an exempted path", pathInfo);
+      return;
+    }
+
+    for (ResourceIsolationPolicy resourceIsolationPolicy : resourceIsolationPolicies) {
+      if (!resourceIsolationPolicy.isRequestAllowed(containerRequest, targetedPage)) {
+        logAtDebug(
+            "Isolation policy {} has rejected a request to {}",
+            resourceIsolationPolicy.getClass().getSimpleName(),
+            pathInfo
+        );
+        throw new AbortWithHttpErrorCodeException(ERROR_CODE, ERROR_MESSAGE);
+      }
+    }
+  }
+
+  @Override
+  public void onEndRequest(RequestCycle cycle)
+  {
+    // set vary headers to avoid caching responses processed by Fetch Metadata
+    // caching these responses may return 403 responses to legitimate requests
+    // or defeat the protection
+    if (cycle.getResponse() instanceof WebResponse)
+    {
+      WebResponse webResponse = (WebResponse)cycle.getResponse();
+      if (webResponse.isHeaderSupported())
+      {
+        webResponse.addHeader(VARY_HEADER, SEC_FETCH_DEST_HEADER + ", "
+            + SEC_FETCH_SITE_HEADER + ", " + SEC_FETCH_MODE_HEADER);
+      }
+    }
+  }
+
+  private static IRequestHandler unwrap(IRequestHandler handler) {
+    while (handler instanceof IRequestHandlerDelegate)
+      handler = ((IRequestHandlerDelegate)handler).getDelegateHandler();
+    return handler;
+  }
+
+  private Optional<IPageRequestHandler> getPageRequestHandler(IRequestHandler handler)

Review comment:
       IMO there is no need to use `Optional` here since the only caller does not use it in functional style, but calls `.isEmpty()` + `.get()`. Using `null` is just fine.

##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/FetchMetadataRequestCycleListener.java
##########
@@ -0,0 +1,157 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.wicket.protocol.http;
+
+import static java.util.Arrays.asList;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_DEST_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_MODE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_SITE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.VARY_HEADER;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.wicket.core.request.handler.IPageRequestHandler;
+import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
+import org.apache.wicket.request.IRequestHandler;
+import org.apache.wicket.request.IRequestHandlerDelegate;
+import org.apache.wicket.request.component.IRequestablePage;
+import org.apache.wicket.request.cycle.IRequestCycleListener;
+import org.apache.wicket.request.cycle.RequestCycle;
+import org.apache.wicket.request.http.WebResponse;
+import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;
+import org.apache.wicket.util.string.Strings;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Fetch Metadata Request Cycle Listener is Wicket's implementation of Fetch Metadata.
+ * This adds a layer of protection for modern browsers that prevents Cross-Site Request Forgery
+ * attacks.
+ *
+ * This request listener uses the {@link DefaultResourceIsolationPolicy} by default and can be
+ * customized with additional Resource Isolation Policies.
+ *
+ * This listener can be configured to add exempted URL paths that are intended to be used cross-site.
+ *
+ * Learn more about Fetch Metadata and resource isolation
+ * at <a href="https://web.dev/fetch-metadata/">https://web.dev/fetch-metadata/</a>
+ *
+ * @author Santiago Diaz - saldiaz@google.com
+ * @author Ecenaz Jen Ozmen - ecenazo@google.com
+ */
+public class FetchMetadataRequestCycleListener implements IRequestCycleListener {
+
+  private static final Logger log = LoggerFactory
+      .getLogger(FetchMetadataRequestCycleListener.class);
+  public static final int ERROR_CODE = 403;
+  public static final String ERROR_MESSAGE = "Forbidden";
+
+  private final Set<String> exemptedPaths = new HashSet<>();
+  private final List<ResourceIsolationPolicy> resourceIsolationPolicies = new ArrayList<>();
+
+  FetchMetadataRequestCycleListener(ResourceIsolationPolicy... additionalPolicies) {
+    this.resourceIsolationPolicies.add(new DefaultResourceIsolationPolicy());
+    this.resourceIsolationPolicies.addAll(asList(additionalPolicies));
+  }
+
+  void addExemptedPaths(String... exemptions) {
+    Arrays.stream(exemptions)
+        .filter(e -> !Strings.isEmpty(e))
+        .forEach(exemptedPaths::add);
+  }
+
+  @Override
+  public void onBeginRequest(RequestCycle cycle)
+  {
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    logAtDebug("Processing request to: {}", containerRequest.getPathInfo());
+  }
+
+  @Override
+  public void onRequestHandlerResolved(RequestCycle cycle, IRequestHandler handler)
+  {
+    handler = unwrap(handler);
+    Optional<IPageRequestHandler> pageRequestHandler = getPageRequestHandler(handler);
+    if (pageRequestHandler.isEmpty()) {
+      return;
+    }
+
+    IRequestablePage targetedPage = pageRequestHandler.get().getPage();
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    String pathInfo = containerRequest.getPathInfo();
+    if (exemptedPaths.contains(pathInfo)) {
+      logAtDebug("Allowing request to {} because it matches an exempted path", pathInfo);
+      return;
+    }
+
+    for (ResourceIsolationPolicy resourceIsolationPolicy : resourceIsolationPolicies) {
+      if (!resourceIsolationPolicy.isRequestAllowed(containerRequest, targetedPage)) {
+        logAtDebug(
+            "Isolation policy {} has rejected a request to {}",
+            resourceIsolationPolicy.getClass().getSimpleName(),
+            pathInfo
+        );
+        throw new AbortWithHttpErrorCodeException(ERROR_CODE, ERROR_MESSAGE);
+      }
+    }
+  }
+
+  @Override
+  public void onEndRequest(RequestCycle cycle)
+  {
+    // set vary headers to avoid caching responses processed by Fetch Metadata
+    // caching these responses may return 403 responses to legitimate requests
+    // or defeat the protection
+    if (cycle.getResponse() instanceof WebResponse)
+    {
+      WebResponse webResponse = (WebResponse)cycle.getResponse();
+      if (webResponse.isHeaderSupported())
+      {
+        webResponse.addHeader(VARY_HEADER, SEC_FETCH_DEST_HEADER + ", "
+            + SEC_FETCH_SITE_HEADER + ", " + SEC_FETCH_MODE_HEADER);
+      }
+    }
+  }
+
+  private static IRequestHandler unwrap(IRequestHandler handler) {
+    while (handler instanceof IRequestHandlerDelegate)
+      handler = ((IRequestHandlerDelegate)handler).getDelegateHandler();
+    return handler;
+  }
+
+  private Optional<IPageRequestHandler> getPageRequestHandler(IRequestHandler handler)
+  {
+    boolean isPageRequestHandler = handler instanceof IPageRequestHandler &&
+        !(handler instanceof RenderPageRequestHandler);
+    return isPageRequestHandler ? Optional.of((IPageRequestHandler) handler) : Optional.empty();
+  }
+
+  private static void logAtDebug(String message, Object... params) {

Review comment:
       IMO this helper method is not needed. Slf4j does not add overhead if `{}` placeholders are used (and they are used!).

##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/FetchMetadataRequestCycleListener.java
##########
@@ -0,0 +1,157 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.wicket.protocol.http;
+
+import static java.util.Arrays.asList;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_DEST_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_MODE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_SITE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.VARY_HEADER;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.wicket.core.request.handler.IPageRequestHandler;
+import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
+import org.apache.wicket.request.IRequestHandler;
+import org.apache.wicket.request.IRequestHandlerDelegate;
+import org.apache.wicket.request.component.IRequestablePage;
+import org.apache.wicket.request.cycle.IRequestCycleListener;
+import org.apache.wicket.request.cycle.RequestCycle;
+import org.apache.wicket.request.http.WebResponse;
+import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;
+import org.apache.wicket.util.string.Strings;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Fetch Metadata Request Cycle Listener is Wicket's implementation of Fetch Metadata.
+ * This adds a layer of protection for modern browsers that prevents Cross-Site Request Forgery
+ * attacks.
+ *
+ * This request listener uses the {@link DefaultResourceIsolationPolicy} by default and can be
+ * customized with additional Resource Isolation Policies.
+ *
+ * This listener can be configured to add exempted URL paths that are intended to be used cross-site.
+ *
+ * Learn more about Fetch Metadata and resource isolation
+ * at <a href="https://web.dev/fetch-metadata/">https://web.dev/fetch-metadata/</a>
+ *
+ * @author Santiago Diaz - saldiaz@google.com
+ * @author Ecenaz Jen Ozmen - ecenazo@google.com
+ */
+public class FetchMetadataRequestCycleListener implements IRequestCycleListener {
+
+  private static final Logger log = LoggerFactory
+      .getLogger(FetchMetadataRequestCycleListener.class);
+  public static final int ERROR_CODE = 403;
+  public static final String ERROR_MESSAGE = "Forbidden";
+
+  private final Set<String> exemptedPaths = new HashSet<>();
+  private final List<ResourceIsolationPolicy> resourceIsolationPolicies = new ArrayList<>();
+
+  FetchMetadataRequestCycleListener(ResourceIsolationPolicy... additionalPolicies) {
+    this.resourceIsolationPolicies.add(new DefaultResourceIsolationPolicy());
+    this.resourceIsolationPolicies.addAll(asList(additionalPolicies));
+  }
+
+  void addExemptedPaths(String... exemptions) {
+    Arrays.stream(exemptions)
+        .filter(e -> !Strings.isEmpty(e))
+        .forEach(exemptedPaths::add);
+  }
+
+  @Override
+  public void onBeginRequest(RequestCycle cycle)
+  {
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    logAtDebug("Processing request to: {}", containerRequest.getPathInfo());
+  }
+
+  @Override
+  public void onRequestHandlerResolved(RequestCycle cycle, IRequestHandler handler)
+  {
+    handler = unwrap(handler);
+    Optional<IPageRequestHandler> pageRequestHandler = getPageRequestHandler(handler);
+    if (pageRequestHandler.isEmpty()) {
+      return;
+    }
+
+    IRequestablePage targetedPage = pageRequestHandler.get().getPage();
+    HttpServletRequest containerRequest = (HttpServletRequest)cycle.getRequest()
+        .getContainerRequest();
+
+    String pathInfo = containerRequest.getPathInfo();
+    if (exemptedPaths.contains(pathInfo)) {
+      logAtDebug("Allowing request to {} because it matches an exempted path", pathInfo);
+      return;
+    }
+
+    for (ResourceIsolationPolicy resourceIsolationPolicy : resourceIsolationPolicies) {
+      if (!resourceIsolationPolicy.isRequestAllowed(containerRequest, targetedPage)) {
+        logAtDebug(
+            "Isolation policy {} has rejected a request to {}",
+            resourceIsolationPolicy.getClass().getSimpleName(),
+            pathInfo
+        );
+        throw new AbortWithHttpErrorCodeException(ERROR_CODE, ERROR_MESSAGE);
+      }
+    }
+  }
+
+  @Override
+  public void onEndRequest(RequestCycle cycle)
+  {
+    // set vary headers to avoid caching responses processed by Fetch Metadata
+    // caching these responses may return 403 responses to legitimate requests
+    // or defeat the protection
+    if (cycle.getResponse() instanceof WebResponse)
+    {
+      WebResponse webResponse = (WebResponse)cycle.getResponse();
+      if (webResponse.isHeaderSupported())
+      {
+        webResponse.addHeader(VARY_HEADER, SEC_FETCH_DEST_HEADER + ", "
+            + SEC_FETCH_SITE_HEADER + ", " + SEC_FETCH_MODE_HEADER);

Review comment:
       Please define a constant for the value. No need to concatenate again and again for every request.

##########
File path: wicket-core/src/main/java/org/apache/wicket/protocol/http/FetchMetadataRequestCycleListener.java
##########
@@ -0,0 +1,157 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.wicket.protocol.http;
+
+import static java.util.Arrays.asList;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_DEST_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_MODE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.SEC_FETCH_SITE_HEADER;
+import static org.apache.wicket.protocol.http.ResourceIsolationPolicy.VARY_HEADER;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+import javax.servlet.http.HttpServletRequest;
+import org.apache.wicket.core.request.handler.IPageRequestHandler;
+import org.apache.wicket.core.request.handler.RenderPageRequestHandler;
+import org.apache.wicket.request.IRequestHandler;
+import org.apache.wicket.request.IRequestHandlerDelegate;
+import org.apache.wicket.request.component.IRequestablePage;
+import org.apache.wicket.request.cycle.IRequestCycleListener;
+import org.apache.wicket.request.cycle.RequestCycle;
+import org.apache.wicket.request.http.WebResponse;
+import org.apache.wicket.request.http.flow.AbortWithHttpErrorCodeException;
+import org.apache.wicket.util.string.Strings;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Fetch Metadata Request Cycle Listener is Wicket's implementation of Fetch Metadata.
+ * This adds a layer of protection for modern browsers that prevents Cross-Site Request Forgery
+ * attacks.
+ *
+ * This request listener uses the {@link DefaultResourceIsolationPolicy} by default and can be
+ * customized with additional Resource Isolation Policies.
+ *
+ * This listener can be configured to add exempted URL paths that are intended to be used cross-site.
+ *
+ * Learn more about Fetch Metadata and resource isolation
+ * at <a href="https://web.dev/fetch-metadata/">https://web.dev/fetch-metadata/</a>
+ *
+ * @author Santiago Diaz - saldiaz@google.com
+ * @author Ecenaz Jen Ozmen - ecenazo@google.com
+ */
+public class FetchMetadataRequestCycleListener implements IRequestCycleListener {
+
+  private static final Logger log = LoggerFactory
+      .getLogger(FetchMetadataRequestCycleListener.class);
+  public static final int ERROR_CODE = 403;
+  public static final String ERROR_MESSAGE = "Forbidden";
+
+  private final Set<String> exemptedPaths = new HashSet<>();
+  private final List<ResourceIsolationPolicy> resourceIsolationPolicies = new ArrayList<>();
+
+  FetchMetadataRequestCycleListener(ResourceIsolationPolicy... additionalPolicies) {

Review comment:
       Why this constructor and the method below are package private ?
   How am I supposed to make use of them in my app ?




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