Told someone I'm working on an 0Auth server/library.

*but that already works/exists, why re-invent the weel?*

Because although it indeed already exists/works, I'd rather re-invent the weel and also throughout the process learn how it works in depth than just using an implementation and not learning much new (when I've got time, of course)!

If the time comes when the traditional signing in with email dies out, I don't know how long I'm gonna last to the Internet anymore. I never liked the idea of having my accounts associated with these giants especially with Facebook.

A day using “0auth”, another day using “OAuth”...

I have a question, let's say I have a website and app both using oAuth facebook login. Should I save the access token provided by facebook in my database and if I should, what will happen to the access token when user logins with facebook on website and then login again with the app? is that mean access token is going to be overwritten by new login? and do you have any other suggestions for 0auth integration?