metamaps--metamaps/app/policies/token_policy.rb

class TokenPolicy < ApplicationPolicy
  class Scope < Scope
    def resolve
      if user
        scope.where('tokens.user_id = ?', user.id)
      else
        scope.where(:id => nil).where("id IS NOT ?", nil) # to just return none
      end
    end
  end

  def create?
    user.present?   
  end

  def my_tokens?
    user.present?
  end

  def destroy?
    user.present? && record.user == user
  end

end