RC2 how can I use the login feature on my own database

I have a postgres database that I already implement in my project that uses an email and password functionality. I already have registration working using my own code now the part I need is this

varresult=await_signInManager.PasswordSignInAsync(model.Email,model.Password,model.RememberMe,lockoutOnFailure:false);if(result.Succeeded){_logger.LogInformation(1,"User logged in.");returnRedirectToLocal(returnUrl);}

Which I got from this https://docs.asp.net/en/latest/security/authentication/identity.html

my question is how can I get

_signInManager.PasswordSignInAsync()

to query against the database that I have, in the Appsetings.json DefaultConnections I already have the correct credentials for my database and everything works. As I can use CRUD methods against my database, I just do not know how to make the SignInManager use that database instead of the default.