27. "libcurl built with GNUTLS ignores the SSLCERT option" - Unlike

  Curl_ossl_connect(), the Curl_gtls_connect() function does not send the user
  certificate to the peer. In fact, it ignores the conn->data->set.cert field
  completely, it always uses the anonymous credentials. See
  http://curl.haxx.se/bug/view.cgi?id=1348930