509_ctx</b> and <b>verify_callback</b> is called with <b>preverify_ok</b>=0. By applying X509_CTX_store_* functions <b>verify_callback</b> can locate the certificate in question and perform additional steps (see EXAMPLES). If no error is found for a certificate, <b>verify_callback</b> is called with <b>preverify_ok</b>=1 before advancing to the next level.</p>

<p>The return value of <b>verify_callback</b> controls the strategy of the further verification process. If <b>verify_callback</b> returns 0, the ve