Can I avoid double registration of my app membership and shopify membership registration?

[takumiendoh]

This is my first time to develop shopify API.
I am developing a smartphone app.
I understand that the storefront API can be used to implement shopping functionality in my smartphone app.

Question
Do I need to register as a member with my own app and then register as a member with shopify when shopping?

My ideal is to purchase products with the membership information of my app.

Is my understanding correct?
Is it possible to avoid double registration?