Only users in the SSO provider's application configuration for Atlan can log in via SSO and have their user profiles created automatically in Atlan.
To restrict access to certain users, edit the list of users configured for Atlan in your SSO provider to a limited set of users.
Each time a new user needs to be onboarded, they will need to be added to this list in your SSO provider before they can access Atlan. Without being added to this list, no user in Atlan will be automatically created even if they attempt to log in.