A simple mu-plugin, provides a static config class for handling Wordpress config globals.
Add into wp-content/mu-plugins directory.
In the custom plugin that will use it:
JbConfig::defined('SOME_GLOBAL'); // false
define('SOME_GLOBAL', 'test');
JbConfig::defined('SOME_GLOBAL'); // true
JbConfig::get('SOME_GLOBAL'); // 'test'
JbConfig::get('SOME_UNDEFINED_GLOBAL', 'default value'); // 'default value'
Currently it only supports defined globals but there's scope for being able to swap out the config driver (e.g if using a .env file), and potentially setter methods etc.