func application(app: UIApplication, openURL url: NSURL, options: [String : AnyObject]) -> Bool {

    // Before doing this, you should check the url is your redirect-uri before doing anything. Be safe :)
    if let components = NSURLComponents(URL: url, resolvingAgainstBaseURL: false),
        queryItems = components.queryItems, 
        code = queryItems.first?.value {

        // Let's find the instance of our authentication controller, 
        // it would be the presentedViewController. This is another 
        // reason to check before that we are actually coming from the SFSafariViewController
        if let rootViewController = window?.rootViewController,
            authenticationViewController = rootViewController.presentedViewController as? AuthenticationViewController {
            authenticationViewController.authenticateWithCode(code)
        }

        return true
    }

    return false
}

let provider = OAuthDribbble(clientId: "your-client-id", 
    clientSecret: "your-client-secret", 
    scopes: ["public", "upload"])

let authenticationViewController = AuthenticationViewController(provider: provider)

authenticationViewController.failureHandler = { error in
    print(error)
}

authenticationViewController.authenticationHandler = { token in
    print(token)

    authenticationViewController.dismissViewControllerAnimated(true, completion: nil)
}

presentViewController(authenticationViewController, animated: true, completion: nil)