When moving between apps assigned to different Sharepoint Realms, the user is requested to re-authenticate. The realm establishes the trust relationship between Okta and the SharePoint application.

• SharePoint Application

This behavior is not exclusive to Sharepoint Realms. When an authentication policy (App Sign On Policy—ASOP) is configured, it verifies that users who try to sign in to the app meet specific conditions and enforces factor requirements based on those conditions. Please refer to Authentication policies for more details.

In the context of a Sharepoint implementation where the realms are defined as individual apps, the Okta authentication layer will persist the login session across realms as long as the authentication policies are the same.  The end user may be prompted to reauthenticate if apps use different authentication policies. 

After the authentication policies are aligned, the authentication and session persistence work seamlessly when moving between apps associated with different realms.