feat: add download-offline-license Maven goal (#22932)

Add a new Maven goal that provides a URL for downloading
an offline license key. Unlike download-license which opens
a browser and downloads the license automatically, this
command displays a machine-specific URL that users can
visit to manually download an offline license.

The offline license is tied to the machine's hardware ID
and must be saved to ~/.vaadin/offlineKeyV2.

Usage: mvn vaadin:download-offline-license

Co-authored-by: Mikhail Shabarov <61410877+mshabarov@users.noreply.github.com>

Author: Artur-

flow-plugins/flow-maven-plugin/src/main/java/com/vaadin/flow/plugin/maven/DownloadOfflineLicenseMojo.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2000-2025 Vaadin Ltd.
+ *
+ * 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.vaadin.flow.plugin.maven;
+
+import java.io.File;
+
+import org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.MojoFailureException;
+import org.apache.maven.plugins.annotations.Mojo;
+
+import com.vaadin.pro.licensechecker.LocalOfflineKey;
+import com.vaadin.pro.licensechecker.MachineId;
+import com.vaadin.pro.licensechecker.OfflineKeyValidator;
+
+/**
+ * Goal that provides the URL to download a Vaadin offline license key.
+ * <p>
+ * This command displays a machine-specific URL that can be used to manually
+ * download an offline license key. The offline license is tied to this
+ * machine's hardware ID and must be saved manually to the file system
+ * (~/.vaadin/offlineKey).
+ * <p>
+ * Unlike the online license (proKey), offline licenses work without internet
+ * connectivity and are suitable for CI/CD environments and offline development.
+ *
+ * @since 25.0
+ */
+@Mojo(name = "download-offline-license", requiresProject = false)
+public class DownloadOfflineLicenseMojo extends FlowModeAbstractMojo {
+
+    @Override
+    protected void executeInternal()
+            throws MojoExecutionException, MojoFailureException {
+        try {
+            MachineId machineId = new MachineId();
+            String offlineUrl = OfflineKeyValidator.getOfflineUrl(machineId);
+
+            // Get the primary offline key location (first in the priority list)
+            File[] locations = LocalOfflineKey.getLocations();
+            String locationPath = locations.length > 0
+                    ? locations[0].getAbsolutePath()
+                    : "~/.vaadin/offlineKeyV2";
+
+            getLog().info("========================================");
+            getLog().info("Vaadin Offline License Download");
+            getLog().info("========================================");
+            getLog().info("");
+            getLog().info(
+                    "To download an offline license for this machine, visit:");
+            getLog().info("");
+            getLog().info("  " + offlineUrl);
+            getLog().info("");
+            getLog().info(
+                    "The offline license will be tied to this machine's hardware ID.");
+            getLog().info("After downloading, save the license file to:");
+            getLog().info("  " + locationPath);
+            getLog().info("");
+            getLog().info(
+                    "For CI/CD build servers, you can download a server license key");
+            getLog().info("that works on any machine from:");
+            getLog().info("  https://vaadin.com/myaccount/licenses");
+            getLog().info("");
+        } catch (Exception e) {
+            throw new MojoFailureException(
+                    "Failed to generate offline license URL", e);
+        }
+    }
+
+}