Creating a WordPress plugin that includes a custom admin menu and license key activation involves several key steps. Follow this comprehensive guide to build your plugin, ensuring it has a user-friendly admin interface and secure license management.

Step 1: Add a new top-level menu for your plugin

To enhance the usability and accessibility of your WordPress plugin, it’s crucial to add a new top-level menu in the WordPress admin dashboard. This menu serves as the entry point for users to access and manage your plugin’s settings and features.

Register the Menu: Use the add_action function to hook into the admin_menu action.

// Hook to add a new admin menu
add_action('admin_menu', 'myplugin_activation_admin_menu');

function myplugin_activation_admin_menu() {
	if(myplugin_is_active()) {
		// Add the menu pages that show if the plugin is active here
	} else {
		// Add a new top-level menu for license key activation
		add_menu_page(
			esc_html__('My Activation Page', 'textdomain'),   // Page title
			esc_html__('My Activation Page', 'textdomain'),   // Menu title
			'manage_options',                                 // Capability required to see the menu
			'myplugin-activation-page',                       // Menu slug
			'myplugin_activation_page_content',     // Function to display the page content
			'dashicons-admin-generic',              // Icon URL or Dashicon class
			20                                      // Position in the menu order
		);
	}
}

Step 2: Function to display the content of the custom admin page

Once the top-level menu is in place, the next step is to create a function that defines the content displayed on your custom admin page. This page allows users to configure plugin settings and view relevant information.

Create the Admin Page Content: Define a function that outputs the HTML for your admin page.

function myplugin_process_form_submission() {
    // Check if the form was submitted
    if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['myplugin_license_key'])) {
        $license_key = sanitize_text_field($_POST['myplugin_license_key']);
        $activation  = myplugin_send_activation_request($license_key);

        // Check if the activation attempt was successful 
        if ($activation['result'] === 'success') {
            update_option('myplugin_is_active_option', true);

            // Redirect to your plugin admin page
            wp_redirect(admin_url('admin.php?page=myplugin-admin-page'));
            exit;
        } else {
            // Set an error message to be displayed on the activation page
            add_option('myplugin_error_message', 'Error: ' . $activation['message']);
        }
    }
}

// Hook the form processing function early to ensure it runs before the page content is rendered
add_action('admin_init', 'myplugin_process_form_submission');

// Function to display the content of the custom admin page
<?php function myplugin_activation_page_content() {
    // Retrieve and delete the error message if it exists
    $error_message = get_option('myplugin_error_message', false);
    if ($error_message) {
        delete_option('myplugin_error_message');
    }

    // Display the admin page content
    ?>
    <div class="wrap">
	<h1><?php esc_html__('Enter License Key', 'textdomain'); ?></h1>

	<?php if (isset($error_message)): ?>
		<div class="notice notice-error is-dismissible">
			<p><?php echo esc_html($error_message, 'textdomain'); ?></p>
		</div>
	<?php endif; ?>

	<form method="post" action="">
		<table class="form-table">
			<tr valign="top">
				<th scope="row"><label for="submitted_text"><?php esc_html__('License Key', 'textdomain'); ?></label></th>
				<td><input type="text" id="license_key" name="myplugin_license_key" value="" class="regular-text" /></td>
			</tr>
		</table>
		<?php submit_button('Activate'); ?>
	</form>
    </div>
    <?php
}

Step 4: Define the function that handles checking whether or not the license key is active

function myplugin_is_active() {
    return get_option('myplugin_is_active_option', false);
}

Step 5: Define the function that sends the license key activation request

Activating a license key is essential for enabling premium features and services within your plugin. This step covers how to create a function that handles the activation process, sending necessary data to the remote server for validation.

Create the Activation Function: This function will be responsible for sending the license key and other required parameters to the licensing server.

function myplugin_send_activation_request($license_key) {
    // The URL of your WordPress website where the plugin is installed
    $post_url = 'https://domain.ltd/'; // Update this with your actual site URL

    // The parameters for the API request
    $parameters = array(
        'fslm_v2_api_request' => 'activate',
        'fslm_api_key'        => '0A9Q5OXT13in3LGjM9F3W', // Your API key
        'license_key'         => $license_key,
        'device_id'           => 'userdomain.ltd' // Update this with your actual device ID
    );

    // Make the HTTP request
    $response = wp_remote_post($post_url, array(
        'body' => $parameters,
        'timeout' => 15,
        'sslverify' => false
    ));

    // Check for errors
    if (is_wp_error($response)) {
        return array('result' => 'error', 'message' => $response->get_error_message());
    }

    // Decode the response
    $body = wp_remote_retrieve_body($response);
    $result = json_decode($body, true);

    // Return the result
    return $result;
}

By following these steps, you can create a robust WordPress plugin with a custom admin menu and secure license key activation. This ensures a seamless user experience and proper license management for your plugin users.

This guide has shown you how to create a WordPress plugin protected with license activation, ensuring that only authorized users can access premium features. Implementing these techniques helps maintain the integrity of your plugin and provides a seamless experience for your users. For more detailed information on each step, refer back to the sections provided, and start building your secure and user-friendly WordPress plugin today.