protect csv file access in static app

In a static web app (nothing except html, css and javascript),
I'm searching for a method to protect a file (e.g. json) from being accessed.

That file should only be accessible by authenticated and approved users. (I don't know yet how authentication will be handled.)

I can hide the view of the content in the application with userapp.io e.g., but I can't prevent someone to read it if he wanted to.

Would this be possible?

I thought of putting the protected file on www.firebase.com, but I could not find any practical example.

I also found solutions with .htaccess, but I need to avoid server dependent solutions.

P.S.: Not asking for code here ;-), just advice to point me in the right direction will do.
Thanks in advance!