json_schema: {
      "$schema": "http://json-schema.org/draft-07/schema#",
      "type": "object",
      "properties": {
          "username": {
              "type": "string",
              "maxLength": 20
          },
          "password": {
              "type": "string",
              "maxLength": 20
          }
      },
      "required": [
          "username",
          "password"
      ],
      "additionalProperties": false
  }