API server for our license key feature. Visit blog posts https://bit.ly/2Vwobsu

api_license_key_server.php

<?php

    // Load up WordPress.
    require_once '../wp-load.php';

    // Include license key funcitons that handle the options.
    require_once 'options.php';

    // Include license key controller functions that handle the routes.
    require_once 'controllers.php';

    // Autoloader for Composer with (all packages and dependencies).
    require_once 'vendor/autoload.php';

    // Get all WordPress users of with role subscriber.
    $users        = array();
    $subscribers  = get_users(['role__in' => ['subscriber']]);

    foreach ($subscribers as $subscriber) {
      $license_key                    = get_license_key($subscriber->user_login);
      $users[$subscriber->user_login] = $license_key['password'];
    }

    // Instantiate Slim PHP framerwork.
    $app = new Slim\App();

    // Basic authentication.
    $app->add(new \Slim\Middleware\HttpBasicAuthentication(array(
        'realm'  => 'Protected',
        // Restricted folder.
        // For your setup may need to add `/api` as your restricted folder.
        'path'   => '/', 
        // Working over HTTPS for improved security.
        'secure' => true,
        // All register users (out of WordPress).
        'authenticator' => function ($args) use($users) {
          
            if (password_verify($args['password'], $users[$args['user']])) {
              return true;
            }
          
            return false;
        },
        // Use to return an error message if the auth fails.
        'error'  => function ($request, $response, $arguments) {

            $data            = [];
            $data['status']  = 'error';
            $data['message'] = $arguments['message'];

            $body = $response->getBody();
            $body->write(json_encode($data, JSON_UNESCAPED_SLASHES));

            return $response->withBody($body);
         }
    )));

    // Grouping API routes.
    // For your setup may need to add `/api` as you group top URL.
    $app->group('/', function() use ($app) {

        // Retrieve license key after authentication.
        $app->post('/license', 'get_license');

        // Activate license key (+1) active_installs and add site URL.
        $app->post('/license/activate', 'activate_license');

        // Deactivate license key (-1) for active installs.
        $app->post('/license/deactivate', 'deactivate_license');
        
        // Development mode only. (remove these paths for production)
        $app->get('/license', 'get_license');
        $app->get('/license/activate', 'activate_license');
        $app->get('/license/deactivate', 'deactivate_license');
    });

    // Run the server app.
    $app->run();