Animate (Track) reflection of Sun onto object

I’m trying to set up a constraint system that will automatically rotate a Mirror plane to reflect a sunbeam onto an object. I think I’m coming close by using two Track To constraints with .5 influence, but could use some help.

My real problem is the reflection beam (Spot light to fake reflection). I could cheat and have this Track To the object but I’d rather like it to be driven by

  • position of sun
  • position of object
  • angle of mirror

Any advice? Thanks,