I'm sure there are ready made password dialogs out there but you can easily make your own - it's just a simple form with few labels, edit boxes and buttons. Tedit has 'PasswordChar' property that you can use to hide the entered password. ( set it to * or similar ). Call the form as a dialog using showmodal so user has to complete it before continuing.
How to implement the actual user management ( hangling & storing users and passwords, objects rights,etc) is a much broader topic.
PS. You have to set the visible property on the password form to false or showmodal will give you an exception.