Adding/Removing claims in ASP.NET Core 2.0

I saw the quick start guides, got authentication and basic role based authorization working in my core 2.0 website.

Is there further documentation on how to add/remove claims from users via code?

There are certain things like subscription:name I would like to add based on whether or not my users have active subscriptions going in Stripe – to create a paid memberships area of my site.

Thanks in advance!