get http://127.0.0.1:8080/gms/overlays/priority
This API returns a JSON object where the key is the priority, and the value of the key is the overlay ID with that priority.
Example:
{ 1 : 2, 2 : 3, 3 : 1 }
This would order the overlays with the overlay with ID 2 first, overlay with ID 3 second, etc.