Unable to test Blob.AttachOnDocument

I wanted to test the Blob.AttachOnDocument operation

• create a batch
• upload a file in the batch
• select a target document
• click on run

The execution fails with a response

{
  "entity-type": "exception",
  "status": 404,
  "message": "com.sun.jersey.api.NotFoundException: null for uri: http://demo.nuxeo.com/nuxeo/site/automation/batch/execute"
}

I am not able to debug further using wget or curl since all calls seem to be rejected (401): there may be some filtering at the reverse proxy level ...