I guess what I'm talking about is not something to identify the reader. It is just identifying the global subscription so the content-holding site can know that

I guess what I'm talking about is not something to identify the reader. It is just identifying the global subscription so the content-holding site can know that it will get credit for the impression. The point is that the content site doesn't have to know who you are and just that they are going to get paid so they can show you the content. Think of it like google/fb login. I can ask for the bare minimum on my site and basically just get a token. It doesn't tell me who you are, but just that you have an ID in the google/fb system.