Swift post nested JSON object

I need to post the JSON object which is nested as below,

{
"params": {
    "City": "",
    "Country": "",
    "Email_Id": "abc@gmail.com",
    "MobileNumber": "1234",
    "UserName": "abc"
},
"userId": 0,
"userAddress": ""
}

How can I create an array or dictionary and pass it to NSURLRequest.