look , never yse that type of auth because anybody on the same computer can know the password by just loking at the history, and generally it is sent unsecured etc. so NEVER USE IT!
you can ask them to loging but not to put their password into the URL, you can use the header function to force the users to login by something like this
header("auth blablala"); /// search for this because I'm not sure , goto w3c and see for headers