hx509_cert_get_attribute
if (hx509_cert_get_attribute(cert, oid) != NULL)
a = hx509_cert_get_attribute(cert, &asn1_oid_id_pkcs_9_at_friendlyName);
a = hx509_cert_get_attribute(cert, &asn1_oid_id_pkcs_9_at_localKeyId);
hx509_cert_get_attribute (