Livy GET requests work but POST requests fail with "401 Authentication required"

["Partridge, Lucas (GE Aviation)" <Lu...@ge.com>]

I've written a Java client for parts of Livy's REST API at https://github.com/apache/incubator-livy/blob/master/docs/rest-api.md#response-body . The client uses Spring's RestTemplate class and the Livy server is secured with Kerberos.

Get /sessions and GET /batches requests work fine. But both POST /sessions and POST /batches requests fail with:
org.springframework.web.client.HttpClientErrorException: 401 Authentication required

Has anyone else seen something like this where the GET requests work but POST requests don't?  Does my username need adding to some Livy config setting perhaps, e.g., to livy.server.access_control.users as described at http://henning.kropponline.de/2016/11/06/connecting-livy-to-a-secured-kerberized-hdp-cluster/ ?

Thanks, Lucas.