adding vertex custom data for game engine shaders I would like to know how you can add data to each vertices so that in unity I can access that data to perform shader calculations?

I was reading a article. https://www.alanzucconi.com/2018/09/17/shader-showcase-saturday-10/#more-10187. on how to perform the fortnite procedural building animations.

There are several data values added to each vertex in the article.


a extra bit (0 or 1) for left and right
pivots and rotation axis are stored in the vertex data
a additional integer for timing calculations


How would I add this data to a model in blender 2.7 or 2.8? Additionally what is this known as in blender? Vertex Data is blank in the blender manual. https://docs.blender.org/manual/en/2.79/modeling/meshes/properties/custom_data.html
So I'm not sure what topic to search for using blender.
I was aware of using vertex colors and I have used them in the past for vertex animations. 
But as there was a need for 3 different data properties I didn't know how to represent the extra detail in the vertex.

I started looking for my answer from the perspective of the shader instead of blender + custom vertex data.

fortnite procedural animation

What this developer did was use a additional UV channel instead.