Introduction to Web Single-Sign-On
Imagine that you visit sears.com, a leading shopping website, or using smartsheet.com, a popular project management web app, and try to log into your accounts there. Here is what you will see (as in Figure 1): Sears allows you to sign in using your Facebook account, and Smartsheet lets the login go through Google. This way of authentication is known as single sign-on (SSO), which enables a user to log in once and gain access to multiple websites without the hassle of repeatedly typing her passwords. Today, leading web technology companies such as Facebook, Google, Yahoo, Twitter, PayPal, and Microsoft all offer SSO services.
Figure 1. Facebook login on Sears and Google login on Smartsheet