Create rules and routing. Note: Only needed if you have 2 interfaces or more.

vi /etc/sysconfig/network-scripts/route-eth0

Add the following

10.0.250.49/16 dev eth0 table 0
default via 80.71.137.49 dev eth0 table 0

vi /etc/sysconfig/network-scripts/rule-eth0

Add the following

iif eth0 table 0
default via 80.71.137.49

yum -y update
yum -y install squid
systemctl start squid
systemctl  enable squid
systemctl status squid

Configuration files are located here.

/etc/squid/squid.conf
/var/log/squid/access.log
/var/log/squid/cache.log

Change the following in /etc/squid/squid.conf

From:

acl localnet src 10.0.0.0/8    		# RFC1918 possible internal network
acl localnet src 172.16.0.0/12 		# RFC1918 possible internal network
acl localnet src 192.168.0.0/16		# RFC1918 possible internal network
acl localnet src fc00::/7      		# RFC 4193 local private network range
acl localnet src fe80::/10     		# RFC 4291 link-local (directly plugged) machines

To:

acl localnet src your_network		# RFC1918 possible internal network
# acl localnet src 172.16.0.0/12 	# RFC1918 possible internal network
# acl localnet src 192.168.0.0/16	# RFC1918 possible internal network
# acl localnet src fc00::/7      	# RFC 4193 local private network range
# acl localnet src fe80::/10     	# RFC 4291 link-local (directly plugged) machines

Also tweak this line from:

http_access deny CONNECT !SSL_ports

To:

# http_access deny CONNECT !SSL_ports

Restart squid and we are done

systemctl  restart squid

Edit the following file /etc/yum.conf

Add the following lines so it looks like this

[main]
 
proxy=http://squid.mgt:3128
# proxy_username=username
# proxy_password=password
 
cachedir=/var/cache/yum/$basearch/$releasever
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
installonly_limit=5
bugtracker_url=http://bugs.centos.org/set_project.php?project_id=23&ref=http://bugs.centos.org/bug_report_page.php?category=yum
distroverpkg=centos-release
 
 
#  This is the default, if you make this bigger yum won't see if the metadata
# is newer on the remote and so you'll "gain" the bandwidth of not having to
# download the new metadata and "pay" for it by yum not having correct
# information.
#  It is esp. important, to have correct metadata, for distributions like
# Fedora which don't keep old packages around. If you don't like this checking
# interupting your command line usage, it's much better to have something
# manually check the metadata once an hour (yum-updatesd will do this).
# metadata_expire=90m
 
# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d

Test if things are working

yum clean all && yum search dovecot

yum -y install httpd-tools

Create a file for the username and password the file also needs to be owned by the squid user.

touch /etc/squid/passwd
chown squid: /etc/squid/passwd
htpasswd /etc/squid/passwd proxyuser

Next configure the squid configuration file so that it accepts username and password authentication

vi /etc/squid/squid.conf

After the ACL section add the following lines

auth_param basic program /usr/lib64/squid/basic_ncsa_auth /etc/squid/passwd
auth_param basic children 5
auth_param basic realm Squid Basic Authentication
auth_param basic credentialsttl 2 hours
acl auth_users proxy_auth REQUIRED
http_access allow auth_users

Restart squid and we are done

systemctl restart squid