feat: add Maven goal to download Vaadin Pro license key (#22784)

Introduces a new 'download-license' goal that automates the process of obtaining a Pro license key through browser-based authentication. The downloaded key is saved to ~/.vaadin/proKey for use in validating commercial Vaadin components.

Author: Artur-

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

@@ -0,0 +1,81 @@
+/*
+ * 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 org.apache.maven.plugin.MojoExecutionException;
+import org.apache.maven.plugin.MojoFailureException;
+import org.apache.maven.plugins.annotations.Mojo;
+
+import com.vaadin.pro.licensechecker.LicenseChecker;
+import com.vaadin.pro.licensechecker.LicenseChecker.DownloadOptions;
+import com.vaadin.pro.licensechecker.LicenseException;
+import com.vaadin.pro.licensechecker.LocalProKey;
+import com.vaadin.pro.licensechecker.Product;
+
+/**
+ * Goal that downloads a Vaadin Pro license key by opening the browser and
+ * waiting for the user to log in.
+ * <p>
+ * The downloaded license key is saved to the local file system
+ * (~/.vaadin/proKey) and can be used for validating commercial Vaadin
+ * components.
+ *
+ * @since 25.0
+ */
+@Mojo(name = "download-license", requiresProject = false)
+public class DownloadLicenseMojo extends FlowModeAbstractMojo {
+
+    private static final String PRODUCT_NAME = "vaadin-maven-download";
+    private static final int TIMEOUT_SECONDS = 300; // 5 minutes
+
+    @Override
+    protected void executeInternal()
+            throws MojoExecutionException, MojoFailureException {
+        String version = getFlowVersion();
+
+        // Check if we already have a proKey
+        if (LocalProKey.get() != null) {
+            getLog().info("A license key already exists at "
+                    + LocalProKey.getLocation());
+            getLog().info(
+                    "Delete the existing key file if you want to download a new one.");
+            return;
+        }
+
+        try {
+            LicenseChecker.downloadLicense(new DownloadOptions(
+                    new Product(PRODUCT_NAME, version), TIMEOUT_SECONDS));
+
+            getLog().info("License key downloaded and saved successfully to "
+                    + LocalProKey.getLocation());
+        } catch (LicenseException e) {
+            throw new MojoFailureException("Failed to download license key", e);
+        }
+    }
+
+    /**
+     * Gets the Flow version from the plugin version.
+     */
+    private String getFlowVersion() {
+        if (mojoExecution != null) {
+            return mojoExecution.getMojoDescriptor().getPluginDescriptor()
+                    .getVersion();
+        }
+        // Fallback version when mojoExecution is not available
+        return "0.0.1";
+    }
+
+}