chromium/chromeos/components/test/data/onc/cellular.onc

{
  "Type": "Cellular",
  "Name": "Test Network",
  "Cellular": {
    "AllowRoaming": true,
    "APN": {
      "AccessPointName": "test-apn",
      "Authentication": "",
      "Username": "test-username",
      "Password": "test-password"
    },
    "AutoConnect": true,
  }
}