updating paid plugins

We run wordpress in a hardened form, in particular we do not allow apache to update PHP files. Instead we update plugins and themes using linux cron twice daily. We’ve just migrated to wp-packages to update our free plugins and themes, previously we ran a python script to download zip files from wordpress.org.
Consequently we can’t run the update plugin provided by The Newsletter Plugin and have to manually copy updates to the paid plugins.
Is there any possibility to provide a composer-based update facility or any other type of password/licence key protected facility that would allow us to automate plugin updates?