I agree with kenji's (dead) comment. I'd rather set up login functionality on my own server. If you use a third party service, their downtime becomes your downtime. Worse, you're injecting another company into your relationship with your users. If that were necessary, I'd choose one the customer was already familiar with, like Google, Facebook or Twitter. Setting up login isn't very difficult and libraries exist for…
Login management should be built into the browsers instead. Imagine a UI where you go to log in and instead of a text/email field for login and a password field you get a drop down with a list of your personas that you’ve created with the option of adding a new one. Under the hood it would use a public/private key pair to authenticate you with the site. Browsers could implement a service that backs up your personas a…
You're suggesting some different backend details, but the UX you describe is already in place.