Hello. I have worked on similar projects, often involving IoT applications. I can configure the Arduino, with the aid of a WiFi/Ethernet module, as a server to listen for HTTP requests from your chosen client, parse the request to get the actual command and act to open or close the relay. You can also send any pre-selected command you want; I'll program the Arduino to act as expected in each case.
Contact me to discuss details. I look forward to working with you.