The basic squid config /etc/squid3/squid.conf
instead of the default config file.
auth_param basic program /usr/lib/squid3/basic_ncsa_auth /etc/squid3/passwords
auth_param basic realm proxy
acl authenticated proxy_auth REQUIRED
http_access allow authenticated
http_port 3128
Setting up a user:
sudo htpasswd -c /etc/squid3/passwords username
and then restart the squid3 by
/etc/init.d/squid3
or systemctl restart squid3.service