Single Sign On is an awesome Jetpack plugin module that allows you to enable you and your users to login/register to your self-hosted WordPress site using WordPress.Com login credentials. If you have Jetpack plugin activated in your WordPress site, you can enable single sign on feature in just one click and unlike to other same purpose plugins, there’s no need of creating any app and get API etc. One click and WordPress.com login will automatically come visible in your WP login page.
If you have Jetpack plugin plugin active on your WordPress site, visit Dashboard -> Jetpack -> Jetpack (Module Page), scroll down and activate ‘Jetpack Single Sign On’ module and you are done.
Once enabled, a “Log in with WordPress.com” option will be added to your existing log in form and your users will be able to log in to or register (if enabled) for your WordPress site with the same credentials they use on WordPress.com. It’s completely safe and secure.