If your Plex server is isolated from the internet, you can use a Forward Proxy (like Squid) to provide restricted access to external resources.
Use the following script to modify your PMS service to include your proxy config
Ross's Plex Server Proxy script
This is actually quite simple. Add the following configuration options to the PMS service file (using the edit command)
systemctl edit plexmediaserver.serviceUse this config
[Service]
Environment="no_proxy=localhost,127.0.0.1,.int.example.com"
Environment="https_proxy=http://forward-proxy.int.example:3128"
Environment="http_proxy=http://forward-proxy.int.example:3128"NOTE: Make sure to include any internal-only resources in the no_proxy variable to prevent PMS from attempting to proxy those connections.