The attached shows how to get the user's loginID automatically and have a 'user' security level type table which you can then utilize to disable/enable/make visible/invisible buttons on the form (as demonstrated).
No need to ever have the user login and the getuser() function can be used as expressions in queries or anywhere you like and will always return the user's windows loginID.
Use it to set the default 'EnteredBy' field in your table so you always know who entered the record.
Or use it to allow certain admin type users to give permissions or security levels to other users to the database.