X509_get_ext_by_NID
int ret = X509_get_ext_by_NID(cert, nid, -1);
X509_get_ext_by_NID(cert, nid, ret) >= 0;
i = X509_get_ext_by_NID(cert, NID_subject_key_identifier, -1);
i = X509_get_ext_by_NID(ctx->issuer_cert, NID_subject_alt_name, -1);
X509_get_ext_by_NID(x, NID_subject_alt_name, -1) >= 0 ||
X509_get_ext_by_NID(x, NID_issuer_alt_name, -1) >= 0) {
i_ext = X509_get_ext_by_NID((X509 *) x, NID_ext_key_usage, -1);
int X509_get_ext_by_NID(const X509 *x, int nid, int lastpos);