multitier_architecture | Daily car rental simulation

Why do you think that this is a good idea? What would you gain by re-writing something like identity?

From the Introduction to Identity on ASP.NET Core

ASP.NET Core Identity:

• Is an API that supports user interface (UI) login functionality.

• Manages users, passwords, profile data, roles, claims, tokens, email confirmation, and more.

It's not just database access. It is also code that manages login functionality, secure token creation, secure password management and much more.

You need to take all of the above into consideration if you create a custom system, have an external auditor to pen-test your solution (even though this is a good idea whatever choice you make), unit test, performance test etc.

All the above is already done. You can easily customize the identity with various hook points too.

BTW, identity uses ef to access the datastore already by default.

Do structure your multilayer application, but leave identity out of it. It is a horizontal concern and it's presence is there to simplify your development and let you worry about your business needs only.