Squid Proxy with basic username and password authentication.

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