mod_auth_external: Make sure processes are killed when Prosody shuts down This is needed because modules aren't unloaded during shutdown. The global server-cleanup event seems appropriate to use here.

<tr>
  <th>What is {x} {op} {y}?</th><td>
    <input name="captcha_challenge" type="hidden" value="{challenge}">
    <input name="captcha_reply" pattern="[0-9]+" required type="number">
  </td></tr>