The Google Play Custom App Publishing API lets your enterprise customers publish private apps (also called custom apps) to their managed Google Play store directly from your EMM console or IDE, eliminating the need for IT admins to access the Google Play Console each time they publish a private app to their organization.

• Apps published through this API are permanently private, meaning they can't be made public. Permanently private apps go through a streamlined verification process—published apps appear in the managed Google Play Store in as little as five minutes, compared to over two hours via the Play Console.
• The only store listing details required to publish an app are its title and default listing language.
• You can use Google Play Developer API to integrate additional private app management features into your user interface.

This site contains detailed guidance on how to integrate private app publishing into your customer-facing EMM console or IDE.