OpenSSL::X509::Extension#value=

static VALUE
ossl_x509ext_set_value(VALUE self, VALUE data)
{
    X509_EXTENSION *ext;
    ASN1_OCTET_STRING *asn1s;

    GetX509Ext(self, ext);
    data = ossl_to_der_if_possible(data);
    StringValue(data);
    asn1s = X509_EXTENSION_get_data(ext);

    if (!ASN1_OCTET_STRING_set(asn1s, (unsigned char *)RSTRING_PTR(data),
                               RSTRING_LENINT(data))) {
        ossl_raise(eX509ExtError, "ASN1_OCTET_STRING_set");
    }

    return data;
}