Final answer:
The two explicit roles are snc_external and snc_internal. These roles provide added security by controlling and restricting user access based on specific roles.
Step-by-step explanation:
The two explicit roles are snc_external and snc_internal. These roles are used to provide added security in a system. By ensuring that no user can have both roles, the system can control and restrict access based on the specific role assigned to each user. For example, a user with the snc_external role may have limited access to certain resources, while a user with the snc_internal role may have broader access.