EXCEL VB & Unix Password Authentication

Let me begin by stating I am new to the world of Excel and VB
programming. I have an inherited Excel application with VB code
that requires the users to login using their Unix(Linux) password
supposedly for updating the database. However, this code does
not work. The code does not verify if the password entered is
correct as it should. Has anyone done this before and can help
me with developing the right code? Or, point me to a previous post of the same topic?

Thanks.