Miters are probably best cut on a good table saw with a premium fence. We like to tilt our blade to 46 degrees (left hand tilt) which allows the outside edges to make better contact and lets the glue squeeze out the inside. You must clamp however to keep a square cabinet.
You could also do this with a shaper. I tried it once with our 1.5 HP unit and I still had trouble feeding the material. And of course, a CNC router would be the ticket.