title: https URL with token parameter : how secure is it?
body: <p>On our site, we provide to users a simulation based on their private information (given through a form). We would like to allow them to get back on their simulation results later, but without forcing them to create a login/password account. </p>
  
  <p>We have thought of sending them an email with a link, from which they could get back their results. But, naturally, we have to secure this URL, because private data is at stake.</p>
  
  <p>So we're intending to pass a token (like a 40 characters combination of letters and digit, or a MD5 Hash) in the URL and to use SSL.</p>
  
  <p>Finally, they would receive an email like that:</p>
  
  <blockquote>
    <p>Hi,<br>
    Get back your results on
    <a href="https://www.example.com/load_simulation?token=uZVTLBCWcw33RIhvnbxTKxTxM2rKJ7YJrwyUXhXn" rel="noreferrer">https://www.example.com/load_simulation?token=uZVTLBCWcw33RIhvnbxTKxTxM2rKJ7YJrwyUXhXn</a></p>
  </blockquote>
  
  <p>What do you think about it? Is it secure enough? What would you advise me for the token generation? What about passing URL parameters in a https request?</p>