How to find which raster pixels are within a buffer geometry using RasterLayer API

[WhereMatters]

Consider this ImageService which is a Land cover raster layer with many classes e.g, forest, water, shrubland. I am trying to use the new RasterLayer API to find which pixels are within the buffer geometry and summarize the areas of forest, water, shrubland within the buffer geometry. Is this possible?

I can see the pixelData, but how does one find which pixel lies within the buffer geometry? and then compute the areas for each class within the buffer geometry.

I did see a similar example being demonstrated in one of the videos at video.arcgis.com (pl see screenshot). Not sure how they did that, any clues?