How do you instruct an iPhone or iPad to use VPN when you are not connected to your home Wi-Fi? I used their former Workflow automation app (now dubbed Shortcuts in iOS12) and it did allow reacting to such an event (going out of range of 1 or more wi-fi networks) but did not realize one of the possible actions was to be able to enable VPN.

Was that what you used? Or was it something else?