Use section access first without any reduction field and verify that it works as expected and that the username, domain, etc. are passing through just fine.
For the reduction fields yes, I would recommend to create a key in the section access which links to another table in the data model and resolves such key. Start with a simple user, one with access to only one of the values in those fields, make sure it works and keep adding more complex users.
Note that what section access does roughly speaking is what you can do in the Desktop using menu File > Reduce Data > Keep Possible Values. So if you add the users table to the script, but without the lines section access / section application, you should be able to select one user and see the required white values for each of the reduction fields this user has assigned.
If you don't, then the reduction table is not working. I would develop this way, instead of enabling section access, until I'm sure all users see what they are expected to see.
NTNAME must coincide with the output of the OSUser() function, which returns the account name as seen by QlikView when any user logs in. In most cases -if not all, this follows that convention: DIRECTORY\ACCOUNT
DIRECTORY usually refers to the name of the user directory, active directory, SSO, LDAP, etc. as it is specified in the QMC > Director Service Connectors > Directory Label or the domain in the case of Windows.