Add a new sheet. Three columns: App_UserName; UserName (For their Password User Name); And PW. If their UserName is the same as their Windows Login Name (App_UserName) You won't need the App_UserName column.
List the names and Passwords.
In the VBA Editor, use the Properties to set that sheet's Visible Property to xlVeryHidden
In the ThisWorkbook Code page
In VBA, Application.UserName returns the windows login name
In the Password UserForm, set GoodPW = True. Anywhere else just use
If Not GoodPW Then
MsgBox "you need to use a Password"
Exit Sub
End If