Attach billboard to entity

Hi there, I have a map with entities (lets say a rectangle). When the user clicks on the surface of an entity, I want to add a billboard to that spot on the surface pointing toward the normal vector / orthogonal (as if the billboard was sticked to that surface like a poster).

Billboards have alignedAxis and rotation properties among others (Billboard - Cesium Documentation) but I don’t know how to configure them to achieve the desired result.

I found a discussion on how to compute the normal vector for a surface but not sure if/how it can be applied here: How to get the Normal Vector of a picked position/point?