int X509_check_akid(X509 *issuer, AUTHORITY_KEYID *akid)
{

    if (!akid)
        return X509_V_OK;

    /* Check key ids (if present) */
    if (akid->keyid && issuer->skid &&
        ASN1_OCTET_STRING_cmp(akid->keyid, issuer->skid))
        return X509_V_ERR_AKID_SKID_MISMATCH;
    /* Check serial number */
    if (akid->serial &&
        ASN1_INTEGER_cmp(X509_get_serialNumber(issuer), akid->serial))
        return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
    /* Check issuer name */
    if (akid->issuer) {
        /*
         * Ugh, for some peculiar reason AKID includes SEQUENCE OF
         * GeneralName. So look for a DirName. There may be more than one but
         * we only take any notice of the first.
         */
        GENERAL_NAMES *gens;
        GENERAL_NAME *gen;
        X509_NAME *nm = NULL;
        int i;
        gens = akid->issuer;
        for (i = 0; i < sk_GENERAL_NAME_num(gens); i++) {
            gen = sk_GENERAL_NAME_value(gens, i);
            if (gen->type == GEN_DIRNAME) {
                nm = gen->d.dirn;
                break;
            }
        }
        if (nm && X509_NAME_cmp(nm, X509_get_issuer_name(issuer)))
            return X509_V_ERR_AKID_ISSUER_SERIAL_MISMATCH;
    }
    return X509_V_OK;
}