How to use ASP.net Core 1 "SignInManager" without EntityFramework

I'm looking to implement ASP.net authentication via the SignInManager but without the EntityFramework. I have built my own database layer using SQLClient and want to just create whatever calls is needed in order to make ASP.net authentication work.

The code I have is as follows (executed from the Startup.cs):

// Add EF services to the services container.
services.AddEntityFramework()
    .AddSqlServer()
    .AddDbContext<OAuthAppDbContext>(opt => opt.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));

// Add Identity services to the services container.
services.AddIdentity<ApplicationUser, ApplicationRole>(options =>
{
    options.Cookies.ApplicationCookieAuthenticationScheme = "ApplicationCookie";
    options.Cookies.ApplicationCookie.AuthenticationScheme = "ApplicationCookie";
    options.Cookies.ApplicationCookie.CookieName = "oAuthInterop";
    options.Cookies.ApplicationCookie.AutomaticChallenge = true;
    options.Cookies.ApplicationCookie.AutomaticAuthenticate = true;
    options.Cookies.ApplicationCookie.DataProtectionProvider = new DataProtectionProvider(new DirectoryInfo("d:\\development\\artefacts"),
        configure =>
        {
            configure.SetApplicationName("TestAuthApp");
            //configure.ProtectKeysWithCertificate("thumbprint");
        });
})
    .AddEntityFrameworkStores<OAuthAppDbContext, int>()
    .AddDefaultTokenProviders();

and I need to remove the Entity Framework reliance (and call my own db methods for gathering user details). Has anyone else done something similar in ASP.net core?

Thanks in advance for any pointers! :-)