// == JSON Login Signature
static func loginUser(_ username:String, password:String, completion: @escaping (_ response: Int) -> Void)
    {
     ...
    }
// ==== UIViewController calling it

APIManager.loginUser(tUsername.text!, password: tPassword.text!) { [weak self] (respStatus: Int) in

            if(respStatus == 200) {
              APIManager.shared.currentUserState = APIManager.UserState.LoggedIn
                DispatchQueue.main.async {
                     self?.newView()
                }

            } else {
                APIManager.shared.currentUserState = APIManager.UserState.LoggedOut
            }
        }