private InstanceIdentity getInstanceIdentity(HttpResponse response) throws IOException {
        InstanceIdentityCredentials entity = readEntity(response, InstanceIdentityCredentials.class);
        return entity.getServiceToken() != null
                    ? new InstanceIdentity(entity.getX509Certificate(), new NToken(entity.getServiceToken()))
                    : new InstanceIdentity(entity.getX509Certificate());
    }
Default implementation of {@link ZtsClient}

@author bjorncs
@author mortent
vespa-athenz/src/main/java/com/yahoo/vespa/athenz/client/zts/DefaultZtsClient.java