hi guys

i'm still new to here and linux .i want to control the access to the internet on the proxy server.For my reading i found out the squid.conf is the file to alter i tried to alter is it as follow :
acl ncsa_users proxy_auth REQUIRED
http_access allow ncsa_users
auth_param basic program /usr/lib/squid/ncsa_auth /etc/squid/squid_passwd

but still now authentication is being request i'm using centos (linux) on the proxy server where could i being going wrong