What method is used for baking grayscale curvature maps
This is how I ended up doing it:
Instead of using vertex colors like most of the solutions I found online, I calculated the angle of each edge, and then used a shader to draw the lines in UV space. This Also gives me control over how thick the lines should be.
In some cases the angle calculated isn't right, but that should be easy to fix.

Here is the project: https://github.com/Jummit/curvature-baker