Add sample to show how to flow external claims and tokens to the local identity

[Eilon]

See aspnet/Security#1538

[blowdart]

Dupe of #6

[HaoK]

You closed the wrong bug @blowdart

[blowdart]

rofl Ok I suck

[Tratcher]

Also show using ClaimActions to map remote user data as claims.

[HaoK]

404105b

[gabosistvanpwc]

I don't think the external claims are copied over to the local identity just the authentication tokens are.

The code below is addressing only the tokens:

if (result.Succeeded)
{
    // Store the access token and resign in so the token is included in the cookie
    var user = await _userManager.FindByLoginAsync(info.LoginProvider, info.ProviderKey);
    var props = new AuthenticationProperties();
    props.StoreTokens(info.AuthenticationTokens);
    await _signInManager.SignInAsync(user, props, info.LoginProvider);
 
    _logger.LogInformation("{Name} logged in with {LoginProvider} provider.", info.Principal.Identity.Name, info.LoginProvider);

   return LocalRedirect(Url.GetLocalUrl(returnUrl));
}

Please correct me if I'm missing something and point me to the code which facilitates the flow of the claims.

Thank you!