You can use the acl directive in Squid to create access control lists based on MAC addresses. For example, to allow access only to devices with a specific MAC address, you can use the following configuration in your Squid configuration file:
acl allowed_macs arp 01:23:45:67:89:ab http_access allow allowed_macs http_access deny all
This configuration will create an access control list called allowed_macs that includes the device with the MAC address 01:23:45:67:89:ab. The http_access directives then allow access only to devices in the allowed_macs list, and deny access to all other devices.
You can also use the arp keyword to create an access control list based on the MAC addresses of devices on your network. For example, the following configuration will allow access only to devices on the same subnet as the Squid proxy:
acl allowed_macs arp /24 http_access allow allowed_macs http_access deny all
This configuration will create an access control list called allowed_macs that includes all devices on the same subnet as the Squid proxy. The http_access directives then allow access only to devices in the allowed_macs list, and deny access to all other devices.
Note that MAC address-based filtering may not be completely reliable, as MAC addresses can be spoofed or changed.