Social login only

[dubik]

I'm trying to figure out how to do only social authentication. I want to use Facebook and Google.
I follow SocialSample, and it's fairly clear what it does. However I do not want to sign in Google principals. I want to get authtoken from Google (or Facebook) and then create my own JwtToken and pass that to client. And I want to sign in my principals, because I may allow to use different social auth providers if email match.
I traced the flow to RemoteAuthenticationHandler.cs.

public virtual async Task<bool> HandleRequestAsync()
...
    await Context.SignInAsync(SignInScheme, ticketContext.Principal, ticketContext.Properties);

Is it possible to let me do the sign in?
Or is the idea that I sign out Google's identity, create my own based on that and sign in again?