[creyes123]

I am planning on doing the same. Development of Mozilla Persona (http://www.mozilla.org/en-US/persona/) has continued, despite Mozilla's lack of funded developers. I looked at it a year ago and the list of open bugs was a bit scary. But it looks much better now.

OAuth 2 is a mess. I would not try to use it without a good library. Thankfully, major websites are moving away from it and onto proprietary APIs that are much cleaner. But nowadays all Facebook really wants to give you is an id that is specific to your app. To get an email address, you have to get permission from Facebook first. Even then, it is not guaranteed that the end user will give it to you. They could have registered using their phone, for example. Having an email address is obviously very valuable.

Stripe payments require an email address. I'm sure other billing systems do, too. So an option is to just grab it when they pay for it. But you still need an email authentication system like Persona on top.

If there are other easy to use systems (for end users and developers) out there like Persona, I would love to hear about them, too.