mod_http_oauth2: Add service documentation URL to metadata This is aimed to those building integrations, so the modules site seems appropriate. Configurable so that a deployment can point to their own OAuth documentation.

<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>