HCP FORM Authentication - Check for SAP employee status

Hi,

I want to ask a short question: Is there a reliable way to determine if a user which passed declarative FORM authentication is an internal SAP employee? I was told to exclude any S-Users from accessing resources, but I want to be sure there aren't any other methods to get through SAP ID service without being an internal SAP employee.

Hope you understand my point.

Kind regards,

Martin