Not sure what exactly the question is. But based on my assumption, you want to know how to do user management in Mendix.
I think you confused with user management within apps and user management within sprintr.
User management for the apps you develop can happen with in the app itself. For which you must use Administration module from app store. Normally this module comes along with project (now-a-days) when you create a new project.
If you really want to use the Mendix accounts to login that is also possible.