How can i offer a single GUI app (trough e.g VNC) that is open to anyone on the internet to control, somewhat safely?

I'd like to make a solution that let's me offer a single Linux GUI app of my choice, e.g an emulator, to be controlled by basically anyone on the internet, trough e.g browser-based VNC. So, i'd like to ask generally what my options are, and also for any recommendations. Some points of importance to me: - The user(s) can't be able to run any other app than the one(s) i've set it to run. - The user(s) can't be able to kill any other processes. *(the ability of quitting the app itself i guess would be impossible to prevent)* - If a user quits the app, either deliberate or accidental, it and only it, must restart automatically. Alternatively, restarting the session. - The user(s) can't be able to drop to shell in any way. - The user(s) can't be able to end the session. - The user(s) can't be allowed to write to any files or dirs, other than the ones necessary for the chosen app. - Remote gamepad control would be nice. Main safety concern would really be to prevent the solution from being used for any nefarious internet activities, since it will be running on a VPS. And i'd rather not have my VPS provider get a reason to yell at me. I'm guessing disabling certain key and keystroke combinations would be part of the solution. Or rather, enabling only certain inputs while disabling *all* other input that are not necessary for operating the app, throughout the running session. **In some way or another**. (any tips on *how to* best do that are appreciated) Love to hear anything what you guys can come up with as to how it could be done. Just some possibly related/useful notes: - https://unix.stackexchange.com/questions/472781/how-to-load-your-own-gui-app-without-the-rest-of-the-gui-in-linux - https://unix.stackexchange.com/questions/512356/is-there-any-way-to-launch-gui-application-without-gui - https://stackoverflow.com/questions/3240633/web-based-vnc-client - https://linux.die.net/man/1/xmodmap - https://unix.stackexchange.com/questions/9061/where-to-apply-xmodmap-for-systemwide-usage - https://en.wikibooks.org/wiki/Guide_to_X11/Starting_Sessions