[Koha] set OPAC to ask for user and password for the first time

How do you set or make changes to the Koha, so that koha will asks the user to input the userID and password before doing anything to access the library system thanks for your help _________________________________________________________________ Is your PC infected? Get a FREE online computer virus scan from McAfee® Security. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963