In the code behind the cmdButton, you could either have an input box or make your own security form and force the user to have authorization before proceding. If their password passes then go ahead with the code and allow the form to open. If it doesn't then pop a message box telling them they do not have authorizations and back out of the cmdButton.
I did a quick search, on this forum, and came up with this. Maybe it will point you in the right direction. If not, try doing a search using "password protect" or just "password.