How to access GLTF userdata?

[quaint pasture]

My game engine (which I am porting from three.js to Bevy) relies heavily on custom user attributes on the materials that set in Blender. This is used for things like outlines, flame effects, billboards and so on.

In three.js these attributes are accessible via material.userData. How can I get access to these attributes in Bevy?

[jolly verge]

This workflow is getting custom data through somehow https://github.com/kaosat-dev/Blender_bevy_components_worklflow, perhaps start there?