mod_sasl2_fast: Fixes to make channel binding work again tls-endpoint isn't a thing that exists. Also, we needed to copy more channel binding state from the primary sasl_handler. Ideally we'd have a cleaner way to do this, but I think that's part of more substantial changes that the SASL API deserves.

<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>