Creating a user with the SDK is simple, I'm sure there's a usable example in the documentation.  Reading information from a database is also simple, there's abundant documentation for that in whatever environment you're working in.  Someone familiar with both technologies could throw together a proof-of-concept in less than an hour.

Beyond that, it depends on your additional requirements.  Is this app supposed to be run just once, or does it add/remove users on an ongoing basis?  How are passwords for new accounts communicated to the users?  Is there a UI?  Can the application define the database schema, or do you need to be able to configure table/column names?  Does an instance of the app need to work with multiple repositories?  Should there be a UI for configuration, or are users technical enough to modify a config file? Etc, etc, etc.

Also could this be a "App"  that can be used for multiple implementations?

I don't see any reason why not.