swift log user in

import UIKit

class LoginViewController: UIViewController {
    
    let domain = "http://plebvote.com:1337"
    let URI = "/order/login"
    
    @IBOutlet weak var usernameTxt: UITextField!
    @IBOutlet weak var passwordTxt: UITextField!
    
    @IBAction func loginTouch (sender: AnyObject) {
        let email : String = usernameTxt.text
        let password : String = passwordTxt.text
        
        if email == "" || password == "" {
            showAlert(title: "Sign in failed", message: "Missing username or password!")
        } else {
            let dict = ["email" : email, "password" : password ]
            post(dict, domain + URI, {( success, results ) in
                if success {
                    NSLog("login successful")
                    
                    var prefs:NSUserDefaults = NSUserDefaults.standardUserDefaults()
                    
                    prefs.setObject(email, forKey : "email")
                    prefs.setObject(password, forKey : "password")
                    prefs.setObject(results["_id"], forKey : "userId")
                    prefs.setObject(results["hash"], forKey : "userHash")
                    prefs.setInteger(1, forKey: "isLoggedIn")
                    prefs.synchronize()
                    
                    self.performSegueWithIdentifier("goToScanner", sender: self)
                } else {
                    self.showAlert(title : "Log in failed", message : toString(results["message"]))
                }
            })
        }
    }
    
    func showAlert (#title : String, message : String) {
        let alert : UIAlertView = UIAlertView()
        
        alert.title = title
        alert.message = message
        alert.delegate = self
        alert.addButtonWithTitle("okay")
        
        alert.show()
    }
    
}

func post(params : Dictionary<String, String>, url : String, done : (success: Bool, results: NSDictionary) -> ()) {
    var request = NSMutableURLRequest(URL: NSURL(string: url)!)
    var session = NSURLSession.sharedSession()
    request.HTTPMethod = "POST"
    
    var err: NSError?
    
    request.HTTPBody = NSJSONSerialization.dataWithJSONObject(params, options: nil, error: &err)
    request.addValue("application/json", forHTTPHeaderField: "Content-Type")
    request.addValue("application/json", forHTTPHeaderField: "Accept")
    
    var task = session.dataTaskWithRequest(request, completionHandler: { data, response, error -> Void in
        var strData = NSString(data: data, encoding: NSUTF8StringEncoding)
        var err: NSError?
        var json = NSJSONSerialization.JSONObjectWithData(data, options: .MutableLeaves, error: &err) as? NSDictionary
        
        if (err != nil) {
            println(err!.localizedDescription)
            done(success : false, results : ["message" : "Unable to parse JSON"])
        } else {
            let s = json["_id"] != nil && json["hash"] != nil
            done(success : s , results : json!)
        }
    })
    
    task.resume()
}