Identify a app connecting, and redirect it based on a identifiant. (mac adress?)

Identify a app connecting, and redirect it based on a identifiant. (mac
adress?)

I am currently trying to create a app which would run 24h/24 7d/7 on a
dedicated computer.
This app must download a file at regular interval. In this app, all is
coded and functionning.
But the link to the file is hardcoded in it, and need to be updated too.
The found solution is to detect when the app connect to the server,
identify it, and redirect him on the new file.
Since there would be hundred of computer, we can t hardcode a new link in
each app, and change the file in the server for each computer, nor point
every computer on the same file since the client may not want all of them
play the same file.
The solution to identify each computer we found was to use the MAC adress,
since it s unique and don t change if the computer is disconnected and
recconnected.
The problem is, how, server side, get the MAC adress of the client?
All solution I ve saw are for browser and are stated as security flaw.
Here, I have no browser, and their is no data to be secure.
I do know pure javascript don t allow this either, but maybe there 's a
node.js module for that that I didn t found?
Or is there other way to identify the computer?
EDIT:
I can get the mac adress in the app, using a node.js module, is there a
way to send it to the server and either get the right file (redirect?) or
the link in some sort I can store it in a variable?
EDIT2:
Since it seems to be important, the computer will be on linux.
Also, is there any way to send a variable from the client to the server in
a html request?