Single Sign On for WordPress is the authentication process that allows a user to access WordPress using a common set of usernames and passwords. This process is typically used in a situation where there is a group of two or more websites that need to use a single username and password.
For the sake of this article, lets say that you have been running a WordPress website for 5 years. You have a product or service that requires a separate domain (possibly a sub domain). The new system requires someone to be logged in to the system in order to access its content.
You could force your users to reauthenticate when they need to access the new system. A better way to approach this is to set up SSO (single sign on) between your main site and the new site. In any SSO setup there is a data source where all your users account information is stored. Since all your users for the past 5 years are on your main website, you will need to make setup your main site as a provider.
A provider is a source that allows others to connect to it and authorize its users for outside services. You can develop a custom API for WordPress to handle the SSO flow or you can install WP OAuth Server. Once your main site is set up as a provider, you will be able to set up your new website to use the users from your main site. The new site is what is known as a client.
SSO can be accomplished by using different authorization protocols. There are many out there that has been specifically designed for SSO. The two options below are the most popular way to perform SSO between two websites.
Both of the protocols above have WordPress plugins available in the WordPress plugin repository. Each protocol above have their pros and cons. Oauth1.0a can be used without a valid SSL/TLS connection but it is hard to set up. OAuth2 replies on SSL/TLS connections to maintain security but again can be a bit complicated. Both of these will help you accomplish Single Sign On for WordPress.
Here at WP Auth Server, we suggest that you use our plugin for making WordPress a OAuth2 Provider. The community version of WP OAuth Server is all you need if you are wanting to setup SSO using your WordPress users for SSO into other websites. If you need more more, you can upgrade to the Pro version.
WP OAuth Server Pro allows you to connect anything to your WordPress site. With WP OAuth Server Pro, you are able to authenticate your users in mobile applications, desktop software as well as other websites. If you are interested in WP OAuth Server Pro, visit https://wp-oauth.com/downloads/wp-oauth-server/.