Use client-side redirects in admin monitors for Chrome (#26207)

Co-authored-by: Daniel Beck <daniel-beck@users.noreply.github.com>
(cherry picked from commit dc03336)

Author: daniel-beck

core/src/main/java/hudson/diagnosis/ReverseProxySetupMonitor.java

@@ -34,6 +34,7 @@
 import java.util.logging.Logger;
 import jenkins.model.Jenkins;
 import jenkins.security.stapler.StaplerDispatchable;
+import jenkins.util.ClientHttpRedirect;
 import org.jenkinsci.Symbol;
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.DoNotUse;
@@ -127,7 +128,7 @@ public HttpResponse doAct(@QueryParameter String no) throws IOException {
             // of course the irony is that this redirect won't work
             return HttpResponses.redirectViaContextPath("/manage");
         } else {
-            return new HttpRedirect("https://www.jenkins.io/redirect/troubleshooting/broken-reverse-proxy");
+            return new ClientHttpRedirect("https://www.jenkins.io/redirect/troubleshooting/broken-reverse-proxy");
         }
     }
 

core/src/main/java/hudson/util/HttpResponses.java

@@ -31,6 +31,7 @@
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.Map;
+import jenkins.util.ClientHttpRedirect;
 import net.sf.json.JSONArray;
 import net.sf.json.JSONObject;
 import org.kohsuke.stapler.HttpResponse;
@@ -51,6 +52,16 @@ public static HttpResponse staticResource(File f) throws IOException {
         return staticResource(f.toURI().toURL());
     }
 
+    /**
+     * Redirect to the given URL via a client-side JS/meta tag redirect.
+     * @param url the URL to redirect to
+     * @return the HttpResponse
+     * @since TODO
+     */
+    public static HttpResponse clientRedirectTo(String url) {
+        return new ClientHttpRedirect(url);
+    }
+
     /**
      * Create an empty "ok" response.
      *

core/src/main/java/jenkins/monitor/JavaVersionRecommendationAdminMonitor.java

@@ -38,12 +38,12 @@
 import java.util.NavigableMap;
 import java.util.TreeMap;
 import jenkins.model.Jenkins;
+import jenkins.util.ClientHttpRedirect;
 import jenkins.util.SystemProperties;
 import org.jenkinsci.Symbol;
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.DoNotUse;
 import org.kohsuke.accmod.restrictions.NoExternalUse;
-import org.kohsuke.stapler.HttpRedirect;
 import org.kohsuke.stapler.HttpResponse;
 import org.kohsuke.stapler.HttpResponses;
 import org.kohsuke.stapler.QueryParameter;
@@ -138,7 +138,7 @@ public HttpResponse doAct(@QueryParameter String no) throws IOException {
             disable(true);
             return HttpResponses.forwardToPreviousPage();
         } else {
-            return new HttpRedirect("https://jenkins.io/redirect/java-support/");
+            return new ClientHttpRedirect("https://jenkins.io/redirect/java-support/");
         }
     }
 

core/src/main/java/jenkins/util/ClientHttpRedirect.java

@@ -0,0 +1,49 @@
+/*
+ * The MIT License
+ *
+ * Copyright (c) 2026, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package jenkins.util;
+
+import hudson.Util;
+import jakarta.servlet.ServletException;
+import java.io.IOException;
+import org.kohsuke.stapler.HttpResponse;
+import org.kohsuke.stapler.StaplerRequest2;
+import org.kohsuke.stapler.StaplerResponse2;
+
+/**
+ * An HTTP response that redirects the client to the given URL.
+ * Unlike {@link org.kohsuke.stapler.HttpRedirect}, this implements a client-side redirect (using meta tag and/or JavaScript).
+ * This allows the redirect to work even when Content Security Policy is enforced in Chrome
+ * (which applies {@code form-action} to redirects after form submission).
+ * @see <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Security-Policy/form-action">MDN documentation on form-action</a>
+ * @see <a href="https://github.com/w3c/webappsec-csp/issues/8">Content Security Policy issue discussing this behavior</a>
+ * @since TODO
+ */
+public record ClientHttpRedirect(String redirectUrl) implements HttpResponse {
+    @Override
+    public void generateResponse(StaplerRequest2 req, StaplerResponse2 rsp, Object o) throws IOException, ServletException {
+        rsp.setContentType("text/html;charset=UTF-8");
+        Util.printRedirect(req.getContextPath(), redirectUrl, redirectUrl, rsp.getWriter());
+    }
+}