This new generally available feature allows web app users to automatically sign in to multiple apps at once.
With Single Sign-On (SSO) for Cloud Directory, you can provide a smooth authentication experience between multiple web applications. If SSO is turned on when a user initially signs in, they are not required to re-enter their credentials the next time they sign in. Instead, they are automatically signed in to any of your apps that are protected by the same App ID instance.
IBM Cloud Single Sign-On (SSO) on Cloud Docs