onDFUFileCreateV2 returns error when trying to write to cloud-based HPCC Cluster

When attempting to write a file to the cloud-based http://10.146.176.14:8010 cluster using the onDFUFileCreateV2 service, the following error occurs:

onDFUFileCreateV2: file signing certificate ('signing' ) not defined in configuration.: Failed to create dfufile

The on-prem mechanism for activating this feature (updating the environment.xml with entries for each cluster/pem and propagating that key to the various clusters) doesn't apply, as apparently the environment.xml file doesn't exist for cloud-based hpcc clusters.

How do we activate this capability for azure clusters? This is needed for the Vault in the Cloud initiative.