Casting Model to ModelGraphics

1. I am using EntityApi and few features from. But ModelGraphics does not contain headers (which i need to add header with authorization) as simple Model (as Model.FromGltf) from PrimitiveAPI. So i need
in some way create Entity from Primitive.

2. Cesium: latest stable, Windows 10, Google Chrome.

It’s not possible to create an entity from a primitive.

I’m trying to see if it’s possible to add headers to the entity api cleanly.