$ charm show cs:~jamesbeedy/prometheus-node-exporter-0 extra-info --format json | jq 
{
  "extra-info": {
    "extra-data": "mydata",
    "extra-inf": "abb58a31e238c85c392ba5f9cb4a0",
    "extra-info": "abb58a31e238c85c392ba5f9cb4a04a70badb8ce"
  }
}