Response body transformer

1

Hello! im trying to change the response to change to camel case to snake, so i change the json body like this:

function _M.transform_json_body(conf, buffered_data)
  local json_body = read_json_body(buffered_data)
  if json_body == nil then
    return
  end
  kong.log.info("transform body", json_body)
  local newJsonBody = {}
  for key,value in pairs(json_body) do
    newJsonBody[toSnake(key)] = value
  end 
  ...

the rest of the code are taking now the newJsonBody table, but it doenst work, i want to do:

   "body": {
        "data": {
            "host": "rxxxxxxxx",
            "clientIp": "xxxxxxxxx",
            "expirationMonth": "09",
            "email": "xxxxxxxxxx",
            "apiKey": "xxxxxxxxxx",
        }
}

to be

   "body": {
        "data": {
            "host": "rxxxxxxxx",
            "client_ip": "xxxxxxxxx",
            "expiration_month": "09",
            "email": "xxxxxxxxxx",
            "api_key": "xxxxxxxxxx",
        }
}

this is my config. yml

config:
  extract:
    body: 
      - "data"
      - "error"

but it doesn work, notice that the key are passing throught a function toSnake. Any helps please.