Download files from Cesium

I am looking for an example of using Cesium as a download service. for example; allowing the user to click and select a building in cesium and then download this building (in what ever format the building is in).

**Context: **

I have a group of buildings in CityGML format and I store them in 3DCityDB and I export them as KML format to visualise them in cesium. I also created a spreadsheet with the id’s and attributes of these building and linked it to the KML files. My aim is to give the user the possibility to select part buildings and download them as KML or Citygml format.

CesiumJS is an front-end library for visualization, so you could use it to have the user click a building an return the id pretty easily. See this picking example for instance.

The downloading service would need to be done somehow on your server side code, Cesium cannot provide that functionality.