Swift: UIViewController Access Control

AccessControl.swift

//
//  AccessController.swift
//  FriendChain
//
//  Created by Ryan Davies on 20/11/2014.
//  Copyright (c) 2014 Ryan Davies. All rights reserved.
//

import UIKit

enum Requirement {
    case Authentication(PFUser?)
    
    func isSatisfied() -> Bool {
        switch self {
        case .Authentication(let user):
            return user!.isAuthenticated()
        }
    }
}

protocol AccessControl {
    class func requirementsForSegue(identifier: String) -> [Requirement]
}

class AccessController {
    func canViewController(viewController: UIViewController, performSegueWithIdentifier identifier: String) -> Bool {
        // this line explodes, so need to rethink pattern
        if let subject = viewController as? AccessControl {
            let requirements = viewController.dynamicType.requirementsForSegue(identifier)
            for requirement in requirements {
                if requirement.isSatisfied() == false {
                    return false
                }
            }
        }
        return true
    }
}

ViewController.swift

// IN THEORY, THIS WOULD BE COOL:

class ViewController: UIViewController, AccessControl {
    class func requirementsForSegue(identifier: String) -> [Requirement] {
        if let segueIdentifier = SegueIdentifier(rawValue: identifier) {
            switch segueIdentifier {
            case .ShowProfile:
                // require the current user to be authenticated!
                return [Requirement.Authentication(User.currentUser())]
            case .SignUp:
                return [Requirement.Authentication(User.currentUser())]
            }
        }
    }
}