NULL.</p>

<p>The <i>flags</i> parameter may be one of the following values.</p>

<p><b>X509V3_ADD_DEFAULT</b> appends a new extension only if the extension does not exist. An error is returned if the extension exists.</p>

<p><b>X509V3_ADD_APPEND</b> appends a new extension, ignoring whether the extension exists.</p>

<p><b>X509V3_ADD_REPLACE</b> replaces an existing extension. If the extension does not exist, appends a new extension.</p>

<p><b>X509V3_ADD_REPLACE_EXISTING</b> replaces an existing extensio