X509_get_key_usage
#define ku_reject(c, u) (!(X509_get_key_usage(c) & (u)))
&& (X509_get_key_usage(cert) & X509v3_KU_DIGITAL_SIGNATURE) == 0) {
uint32_t X509_get_key_usage(X509 *x);
ex_kusage = X509_get_key_usage(c->pkeys[SSL_PKEY_ECC].x509);
if (!(X509_get_key_usage(x) & X509v3_KU_DIGITAL_SIGNATURE)) {