{
    "$schema": "http://json-schema.org/draft-07/schema",
    "type": "object",
    "properties": {
        "foo": {
            "type": "object", 
            "properties": {
                "bar": {
                    "type": "string"
                }
            },
            "required": ["bar"]
        }
    },
    "required": ["foo"],
    "additionalProperties": true
}