Email login activation link for signing into a sight

Not just for activating an account.

http://qz.com/234901/the-future-of-passwords-really-is-no-passwords/

“Sign-in is the part of the site of the site no one cares about. It’s not a feature; it’s a necessary evil. So the question is how do we make that as painless as possible,” says Blaine Cook, formerly of Twitter and now a co-founder of Poetica, a collaborative-writing tool.

It is worth thinking about what exactly a password proves, Cook says. When you forget your password, as you inevitably will, any web service will send you an email for you to reset it. All a password boils down to is being able to prove that you have access to your stated email account. Why not cut out the middleman?

But Cook’s way of doing it is different: Rather than remind users that they have to sign in, Poetica removes the the ugly bits. The first time a user visits Poetica after the initial registration, all she has to do is enter her email address. Since people tend to be logged in to their Gmail or Facebook accounts in any case, the system checks to confirm their logged-in identity on those services and then lets them in. “We can do that without prompting for a password, or any user intervention at all, in most cases for existing users,” Cook says.