That part is easy...just require logins and don't serve the content at all unless they are authorized to see it.
Re:How Bitcoin Can Save Publishing
by jacques_chester on Wednesday October 09, 2013 @10:18PM
(#6525302)
You're thinking of paywalls; it's a different model.
The main problem is reliably identifying who is a legitimate subscriber. I happen to have a robust solution for that problem which this margin is too small to contain.