Shelf offers single-sign-on (SSO) capability for Google users. To enable this feature, navigate to the Profile Settings page, located in the dropdown in the top right hand corner of the application, next to your Avatar.
Once on this page, scroll to the bottom and slide the toggle in the Login Service section to the right. You will need to complete an authentication process if you have not already authenticated your Google account, but once complete you’ll be able to login without having to type in a username/password (assuming you are logged in to Google in your browser).
Simply click on Google logo in the Sign in with Google area of your Shelf login page and you’ll be redirected to your dashboard.