Most websites need user login in order to provide personalized content to visitors. The usual way is to request user to register an user account.Actually, this is not so appealing since if we need to remember one password for each website, it's troublesome, while for developers, it's their responsibility to protect password, once password is leaked, then it's a big headache to a website's business and reputation.So long time ago people started thinking about password-less login, this is a big release for both users and websites. We discuss some common ways of password-less login.1. OpenIDOpenI...