在CanCan中访问get参数

class ApplicationController < ActionController::Base

  ...

  def current_ability
    @current_ability ||= Ability.new(current_user, params[:token])
  end

end

class Ability
  include CanCan::Ability

  def initialize(user, token=nil)
    ...
    can :read, Article, :tokens => { :token => token }
    ...
  end

end