Write To File on server from HTML?

Hi everyone,

I recently added a function to my project to enable File Writing from blueprint (using this post : Save a text file using Blueprints - Plugins - Unreal Engine Forums).

However my game will at the end be hosted on a web server, and it seems that it can’t write anywhere.
How to define a relative path to the .cpp file to save the file to ?
Is that only possible ? I heard one day that hosted application couldn’t write on a server, is that true ?

The questions is still actual, but I asked another point of view there : Save infos via html - Platform & Builds - Unreal Engine Forums