ossl_x509_check_private_key
if (!ossl_x509_check_private_key(pub, pkey))
return ossl_x509_check_private_key(xk, pkey);
return ossl_x509_check_private_key(X509_REQ_get0_pubkey(req), pkey);
int ossl_x509_check_private_key(const EVP_PKEY *k, const EVP_PKEY *pkey);