AppDelegate

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
        self.window = UIWindow(frame: UIScreen.mainScreen().bounds)

        let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
        var loginViewController:LoginVC = mainStoryboard.instantiateViewControllerWithIdentifier("loginVC") as! LoginVC
        var timelineViewController:TimelineVC = mainStoryboard.instantiateViewControllerWithIdentifier("timeline") as! TimelineVC
        
        let login = KeychainInfo.login
        let auth_token = KeychainInfo.auth_token
        
        var launchScreenVC = UIViewController(nibName: "LoadingLaunchScreen", bundle: nil)
        self.window?.rootViewController = launchScreenVC
        
        if (login != nil && auth_token != nil) {
            let parameters:[String: AnyObject] = [
                "login": login!,
                "token": auth_token!,
                "timezone": NSTimeZone.localTimeZone().name
            ]
            // Check if the login and auth_token are valid for the user
            request(.POST, ApiLink.sign_in, parameters: parameters, encoding: .JSON)
                .responseJSON { (_, _, mydata, _) in
                    if (mydata != nil) {
                        let json = JSON(mydata!)
                        if (json["success"].intValue == 1) {
                            // Activate the Background Fetch Mode to Interval Minimum
                            UIApplication.sharedApplication().setMinimumBackgroundFetchInterval(
                                UIApplicationBackgroundFetchIntervalMinimum)
                             self.window?.rootViewController = timelineViewController
                        } else {
                            KeychainInfo.login = nil
                            KeychainInfo.auth_token = nil
                            self.window?.rootViewController = loginViewController
                        }
                    } else {
                        self.window?.rootViewController = loginViewController
                    }
            }
        } else {
          // GOES HERE SOMETIMES WHY??
            self.window?.rootViewController = loginViewController
        }
        
        self.window?.makeKeyAndVisible()
           
        return FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)
}

loginViewController

let parameters:[String: AnyObject] = [
    "login": self.loginTextField.text,
    "password": self.passwordTextField.text,
    "timezone": NSTimeZone.localTimeZone().name
]

request(.POST, ApiLink.sign_in, parameters: parameters, encoding: .JSON)
    .responseJSON{ (_, _, mydata, _) in
        //convert to SwiftJSON
        let json = JSON(mydata!)
        
        if (json["success"].intValue == 0) {
            // ERROR RESPONSE FROM HTTP Request
            GlobalFunctions().displayAlert(title: NSLocalizedString("Authentication_failed", comment: "Authentication Failed"), message: json["message"].stringValue, controller: self)
        } else {
            // SUCCESS RESPONSE FROM HTTP Request
            let login:String! = json["login"].string
            let auth_token:String! = json["auth_token"].string
            
            // Save login and auth_token to the iOS Keychain
            KeychainInfo.login = login
            KeychainInfo.auth_token = auth_token

            // Activate the Background Fetch Mode to Interval Minimum
            UIApplication.sharedApplication().setMinimumBackgroundFetchInterval(
                UIApplicationBackgroundFetchIntervalMinimum)
            
            // Goes to TimelineViewController
            self.performSegueWithIdentifier("homeSegue", sender: self)
        }
}