mod_rest: Catch one (1) reply to a POST-ed stanza from an internal source This will primarily cover error replies, and only those generated by the same Prosody instance using the `origin.reply()` method.

<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>