Hi Victor

The best way to do this is through assigning permissions to a role that you add based on the Authenticated user role.

The role would need to be able to be applied at a course level context and then enrol these users in the course with this role

The permissions that need to be added to the role include the View grades of other users,, view course completion report and any other permissions in the course you may want this role to have. Test this role fully before using it to see that it does what you want.

You may also be interested in creating reports and restricting access to this role.

Regards