FireBaseHelper.fireBaseHelper.BASE_REF.authWithOAuthProvider("facebook", token: "123") { (error, data) -> Void in

        APP_DELEGATE.hideActivityIndicator()
        if error != nil {
            print(error)
            self.loginErrorAlert("Oops!", message: "Check your username and password.")
        } else {

            // Be sure the correct uid is stored.

            NSUserDefaults.standardUserDefaults().setValue(data.uid, forKey: "uid")

            // Enter the app!

            self.performSegueWithIdentifier("CurrentlyLoggedIn", sender: nil)
        }
    }

let username = usernameField.text
    let email = emailField.text
    let password = passwordField.text

    if username != "" && email != "" && password != "" {

        APP_DELEGATE.showActivityIndicator()

        FireBaseHelper.fireBaseHelper.BASE_REF.createUser(email, password: password, withValueCompletionBlock: { error, result in



            if error != nil {
                 APP_DELEGATE.hideActivityIndicator()
                // There was a problem.
                self.signupErrorAlert("Oops!", message: "Having some trouble creating your account. Try again.")

            } else {

                // Create and Login the New User with authUser
                FireBaseHelper.fireBaseHelper.BASE_REF.authUser(email, password: password, withCompletionBlock: {
                    err, authData in

                    let user = ["provider": authData.provider!, "email": email!, "username": username!]

                      FireBaseHelper.fireBaseHelper.USER_REF.childByAppendingPath(authData.uid).setValue(user, withCompletionBlock: { (error, firebase) -> Void in

                        if error != nil {
                             APP_DELEGATE.hideActivityIndicator()
                            self.signupErrorAlert("Oops!", message: "Having some trouble creating your account. Try again.")

                        }else
                        {
                             APP_DELEGATE.hideActivityIndicator()
                            // Store the uid for future access - handy!
                            NSUserDefaults.standardUserDefaults().setValue(result ["uid"], forKey: "uid")

                            // Enter the app.
                            self.performSegueWithIdentifier("NewUserLoggedIn", sender: nil)

                        }
                      })
                })
           }
        })

    }else
    {
        signupErrorAlert("Oops!", message: "Don't forget to enter your email, password, and a username.")
    }

class FireBaseHelper: NSObject {

    static let fireBaseHelper = FireBaseHelper()

    private var _BASE_REF = Firebase(url: "https://poc-demoApp.firebaseio.com")
    private var _USER_REF = Firebase(url: "https://poc-demoApp.firebaseio.com/users")
 var BASE_REF: Firebase {
        return _BASE_REF
    }

    var USER_REF: Firebase {
        return _USER_REF
    }

 var CURRENT_USER_REF: Firebase {
        let userID = NSUserDefaults.standardUserDefaults().valueForKey("uid") as! String

        let currentUser = Firebase(url: "(BASE_REF)").childByAppendingPath("users").childByAppendingPath(userID)

        return currentUser!
    }
}

let credential = FacebookAuthProvider.credential(withAccessToken: FBSDKAccessToken.current().tokenString)

Auth.auth().signIn(with: credential) { (user, error) in
      if let error = error {
        print("Facebook authentication with Firebase error: ", error)
        return
      }
      print("User signed in!") // After this line the Facebook login should appear on your Firebase console
    }