title: PerformSegue in StoryBoard
body: <p>I am working for the first time on storyboard using Swift. 
  In the first page of the app user will login and when login is done successfully, user will navigate to next page. 
  But When button is clicked firstly navigation occurs then after web service gets called, but what I want is to authenticate the Login Web service first then navigate with login data to next page.</p>
  
  <p>I have put the identifier on the login button i.e, "login_success" on the button in storyboard and called self.performSegueWithIdentifier, when login is successfull.</p>
  
  <p>Please guide me. Thanks.</p>