You can learn about the SSO world in depth through our blog post, but briefly:
With single sign-on (SSO), users are authenticated only once, regardless of how many other applications they attempt to access after the initial login. In general, this is achieved when the SSO Identity Provider (IDP) sends the target applications an assertion that the user has been authenticated and should be trusted by that application.
With centralized authentication, the authentication process is different. Once a user has logged into Application 1, logging into App 2 doesn’t feel automatic. Even though the required credentials are identical, the user would still need to enter her authentication information again.
Stormpath Supports Both
1) SSO is available using Stormpath Hosted Login Pages (http://docs.stormpath.com/guides/using-id-site/), which provides and hosts all the common frontend components of user management: Registration pages, login pages, password reset functionality, and more.
In addition to making it easier to get your app off the ground, Hosted Login also enables Stormpath to share authentication across your applications. If you’re interested in getting started with SSO, Hosted Login is currently available on our Lite tier and above (https://stormpath.com/pricing/).
2) Centralized authentication is incredibly simple to enable. Just map a Directory to multiple Applications in Stormpath. Stormpath is designed to be many-to-many, so there’s no limit on the number of mappings you can create. For more information about Account Store Mapping, please refer to the docs: