Standardized permission saving

Hello,

I'm currently working a project to sandbox AppImages and I was
wondering if there was any existing generic standard way for
applications to request system permissions (eg: xdg-downloads from
filesystem, dri from devices), or any up and coming plans for
something the like? The solution I'm currently using is to extend the
XDG desktop entry.

(example file)
[Desktop Entry]
...
[X-AppImage-Required-Permissions]
Files=xdg-download:ro;
Devices=dri;input;
Sockets=x11;wayland;pulseaudio;

I'm aware of xdg-desktop-portal, but that appears to only apply to
on-the-fly and not predetermined permissions. Thanks in advance