It seems it is not really straightforward…
See: https://developer.blender.org/T55333
There are two parts:
- An SSAO pass using Alchemy Obscurance algorithm: https://faculty.digipen.edu/~gherron/references/References/AmbientOcclusion/VV11AlchemyAO.pdf
- An additional screen space pass: Screen Space Curvature in Workbench Engine for better surface detail visualization. Right-Click Select — Blender.Community
Step 2 is not too difficult (there is a .blend file that describes the computation), but step 1 may be more involved…
For step 1, maybe the existing SSAO2 pipeline can be used.
[EDIT]
For completeness, and if someone wants to tackle this, here are the relevant changes done in Blender to support this feature (the SSAO2 pipeline does not use the same algorithm than the one used in 1.):
[/EDIT]