Apache jMeter - Get field name from JSON extractor

I'm using Apache jMeter 5.3. I have a HTTP request which returns JSON response like this:

{
 "result": {
   "certificates": {
     "4b89aa6c131": "MIID2zCC...",
     "ab19aa6c144": "MIID0zCC..."}
  }
}

Is there any way to extract first field name from "certificates" object ("4b89aa6c131" in this example) using JSON Extractor?