mod_http_oauth2: Do minimal validation of private-use URI schemes Per draft-ietf-oauth-v2-1-08#section-2.3.1 > At a minimum, any private-use URI scheme that doesn't contain a period > character (.) SHOULD be rejected. Since this would rule out the OOB URI, which is useful for CLI tools and such without a built-in http server, it is explicitly allowed.

<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>