Identifying Arduino/ESP in close proximity via web controller ie Local WiFi

Hi Folks,
I’m hoping someone can offer some insights / ideas / examples or hints on how to tackle this problem, any suggestion would be appreciated even if its a bit of an out of the box solution.

Question:
I’m looking for a way to identify if Arduino/ESP devices (or maybe specific mac addresses) are on the same local network from a client web browser.

Purpose:
To restrict Arduino control access to users in close proximity only but still using remote hosted database of configurations & web server hosting control webpage.

Current Configuration:
Outputs (eg lights) ← ESP01 (Web client) <INTERNET> WebServer (LAMP stack) hosting output configuration DB <INTERNET> User access to control web page allowing selection of outputs configuration.

Current Functionality:
Any remote or local user with access to the website can select the configuration which is passed to the output.

Update: Possible Solution??:
It looks like a possible solution maybe a “bonjour service”.
But this raises some extra questions is there an bonjour service implementation small enough for an ESP01

Bonus Question:
Does anyone have an example of pushing commands to an arduino / ESP from a web server rather than pulling from the webserver as part of the basic loop()?
Pull solves the problem but tends to lag a bit with the refresh timing of the loop

Update: Possible Solution Bonus Question??:
Maybe either websockets or comet maybe the solutions, sound like more research is required. I’ll update this if I find some info for any one whom follows. If you have some links you would recommend for implementing this please add to the discussion

Thanks for reading, I look forward to your insights!