ruby on rails - Devise allow access to protected url with link -

i developing application requires users logged in - want allow them share particular information others - provided have correct link.

i using devise, , check current_user has 'purchased' object viewing.

it has come in conversations emailed person view information - not them have access account.

ie.

unless current_user   redirect_to "/" , return  end 

i imagine simple auth token in url can check , allow them access if correct?

unless current_user or invalid_auth   redirect_to "/" , return  end 

what best way generate , store auth token , best implementation method

cheers