Convert cUrl command to HTTP Request in Swift

I am building an app that checks domain availability. Right now, I am using the goDaddy API; according to goDaddy, the way to check URL availability is by the following cURL command:

curl -X GET -H "Authorization: sso-key {API_KEY}:{API_SECRET}" "https://api.godaddy.com/v1/domains/available?domain=example.guru"

Right now, I am trying to translate that cURL command to Swift. I am using Alamofire; however, when I make a request, an error as the following shows up:

Credentials must be specified

I was wondering how to solve this problem. Here is my current code:

class ViewController: UIViewController {

    let key = "KEYKEYKEY"
    let secret = "SECRETSECRET"

    var headers: HTTPHeaders = [:]

    override func viewDidLoad() {
        super.viewDidLoad()

        let credential = URLCredential(user: key, password: secret, persistence: .forSession)

        Alamofire.request("https://api.godaddy.com/v1/domains/available?domain=example.guru")
            .authenticate(usingCredential: credential)
            .responseJSON { response in
                debugPrint(response)
        }

        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}