Look
here[
^] for some info on how the application should be structured.
You need to add a library or classes to the Utilities block. I'm pretty sure .Net has classes for authentication, but you could also use the login credentials to get the user rights from the database. Store those in a dictionary with the unique login credential as key (and keep the (succesful) login credential in a session object.) and the user rights as value. Then you can retrieve the user rights at any given time in your application by passing the session object to the library.
This is just a quick example there are many variations.
Hope this helps.
PS: consider giving users roles and use the roles to define the user rights.