xform

     the client <em>has to</em> present a valid Certificate</li>

<li><strong>optional_no_ca</strong>:

     the client may present a valid Certificate<br />

     but it need not to be (successfully) verifiable.</li>

     but it need not to be (successfully) verifiable. This option

     cannot be relied upon for client authentication.  </li>

</ul>

<p>In practice only levels <strong>none</strong> and

<strong>require</strong> are really interesting, because level

<strong>optional</strong> doesn't work with all browsers and level

<strong>optional_no_ca</strong> is actually against the idea of

authentication (but can be used to establish SSL test pages, etc.)</p>

<div class="example"><h3>Example</h3><pre class="prettyprint lang-config">SSLVerifyClient require</pre>

</div>