How to mount CA file for nomad gateway stanza

We are deploying a terminating gateway in our nomad cluster. Some of the services that the gateway proxy to, is using HTTPS. Looks like the gateway stanza in nomad supports passing a ca file.

The documentation says that the file must be accessible to the gateway task. So we decided to volume mount the CA file to gateway task. But the sidecar_task stanza in nomad does not have volume mount option.

What is the right way to pass the CA file to the gateway task?