Sample plugin that utilizes the Digital License Manager PRO theme activator and update server.
Digital License Manager PRO update server is pretty simple to integrate in any plugin, this is just an example with composer support.
The main functionality resides in includes/Bootstrap.php. The setup_updater() method in this class contains information like the API url, credentials, etc.
To install the composer autoloader and packages run:
composer install
This is basic sekeleton for a plugin with Composer support. You can continue developing your own based on this, just change the namespace and etc.