16.2. Setting up Squid as a Caching Proxy With LDAP Authentication

# yum install squid

1. To configure the basic_ldap_auth helper utility, add the following configuration entry to the top of /etc/squid/squid.conf:

   auth_param basic program /usr/lib64/squid/basic_ldap_auth -b "cn=users,cn=accounts,dc=example,dc=com" -D "uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com" -W /etc/squid/ldap_password -f "(&(objectClass=person)(uid=%s))" -ZZ -H ldap://ldap_server.example.com:389

   The following describes the parameters passed to the basic_ldap_auth helper utility in the example above:
   • -B base_DN sets the LDAP search base.
   • -D proxy_service_user_DN sets the distinguished name (DN) of the account Squid uses to search for the authenticating user in the directory.
   • -W path_to_password_file sets the path to the file that contains the password of the proxy service user. Using a password file prevents that the password is visible in the operating system's process list.
   • -f LDAP_filter specifies the LDAP search filter. Squid replaces the %s variable with the user name provided by the authenticating user.
     The (&(objectClass=person)(uid=%s)) filter in the example defines that the user name must match the value set in the uid attribute and that the directory entry contains the person object class.
   • -ZZ enforces a TLS-encrypted connection over the LDAP protocol using the STARTTLS command. Omit the -ZZ in the following situations:
     • The LDAP server does not support encrypted connections.
     • The port specified in the URL uses the LDAPS protocol.
   • The -H LDAP_URL parameter specifies the protocol, the host name or IP address, and the port of the LDAP server in URL format.
2. Add the following ACL and rule to configure that Squid allows only authenticated users to use the proxy:

   acl ldap-auth proxy_auth REQUIRED
   http_access allow ldap-auth

   Important

   Specify these settings before the http_access deny all rule.
3. Remove the following rule to disable bypassing the proxy authentication from IP ranges specified in localnet ACLs:

   http_access allow localnet

4. The following ACL exists in the default configuration and defines 443 as a port that uses the HTTPS protocol:

   acl SSL_ports port 443

   If users should be able to use the HTTPS protocol also on other ports, add an ACL for each of these port:

   acl SSL_ports port port_number

5. Update the list of acl Safe_ports rules to configure to which ports Squid can establish a connection. For example, to configure that clients using the proxy can only access resources on port 21 (FTP), 80 (HTTP), and 443 (HTTPS), keep only the following acl Safe_ports statements in the configuration:

   acl Safe_ports port 21
   acl Safe_ports port 80
   acl Safe_ports port 443

   By default, the configuration contains the http_access deny !Safe_ports rule that defines access denial to ports that are not defined in Safe_ports ACLs.
6. Configure the cache type, the path to the cache directory, the cache size, and further cache type-specific settings in the cache_dir parameter:

   cache_dir ufs /var/spool/squid 10000 16 256

   With these settings:
   • Squid uses the ufs cache type.
   • Squid stores its cache in the /var/spool/squid/ directory.
   • The cache grows up to 10000 MB.
   • Squid creates 16 level-1 sub-directories in the /var/spool/squid/ directory.
   • Squid creates 256 sub-directories in each level-1 directory.
   If you do not set a cache_dir directive, Squid stores the cache in memory.

1. Create the cache directory:

   # mkdir -p path_to_cache_directory

2. Configure the permissions for the cache directory:

   # chown squid:squid path_to_cache_directory

3. If you run SELinux in enforcing mode, set the squid_cache_t context for the cache directory:

   # semanage fcontext -a -t squid_cache_t "path_to_cache_directory(/.*)?"
   # restorecon -Rv path_to_cache_directory

   If the semanage utility is not available on your system, install the policycoreutils-python-utils package.

# echo "password" > /etc/squid/ldap_password
# chown root:squid /etc/squid/ldap_password
# chmod 640 /etc/squid/ldap_password

# firewall-cmd --permanent --add-port=3128/tcp
# firewall-cmd --reload

# systemctl start squid

# systemctl enable squid

# /usr/lib64/squid/basic_ldap_auth -b "cn=users,cn=accounts,dc=example,dc=com" -D "uid=proxy_user,cn=users,cn=accounts,dc=example,dc=com" -W /etc/squid/ldap_password -f "(&(objectClass=person)(uid=%s))" -ZZ -H ldap://ldap_server.example.com:389

user_name password