First, ASP.NET Identity and OWIN are not "separable". OWIN is a standard interface, and ASP.NET Identity is an implementation that deals with users in your application. ASP.NET Identity may or may not follow OWIN, because it works with it, but it can use another pattern as well, no problem.
Second, to reimplement the behavior of ASP.NET Identity, you will need to reimplement the following classes:
Once this is done, your system can work with ASP.NET Identity at the DAL level.
The problem is that by putting an extra layer you will be creating a complicator, since the application is implemented using an agnostic model of data access with dynamic binding to libraries like the Entity Framework.
Are you sure you want to do this? Look, I’ll even answer, but I don’t recommend you go down this path.
– Leonel Sanches da Silva