I have created an organization and connected it to my authentication database with “Membership on Authentication” enabled, but I am not getting users added to the organization.
The automatic membership feature requires the login to be carried out within the context of an Organization (i.e. an Organization parameter was passed to /authorize, or you enable the Org prompt for the application). Otherwise, it is just treated as a normal login on that connection.
Using the Organization parameter in logins:
Custom Development with Organizations
Changing default application behavior for Organizations:
Define Organization Behavior