If you're confused between SSO and centralized authentication mechanism go through these articles to get basic understanding. They help you to understand the difference between two and when to use what. This will also provide you insights on when you've to opt for which kind of approach and solution.
SSO as such doesn't maintain its own user repository and relies on the application for user management services. Centralized authentication services maintain user data repository which can be shared across applications (ex: LDAP, AD). SSO technique issues and validate taken, its mainly performing assertions based on protocols like SAML, JWT or OpenID connect.