def create_guest_user
  u = User.new(:name => "guest", :email => "guest_#{Time.now.to_i}#{rand(100)}@example.com", guest: true)
  u.save!(:validate => false)
  cookies.signed.permanent[:guest_user_id] = u.id
  u
end

response.set_cookie(:guest_user_id, {
  value: u.id,
  path: '/',                 # cookie remains all pages in this domain
  expires: 2.weeks.from_now, # cookie expires after 2 week
  httponly: true,            # prevent javascript modify this cookie
})