One use case for this tool is to be able to run a one off command referencing the variables.
cf-vault exec test -v -- curl -sv -H "X-Auth-Key: $CLOUDFLARE_API_KEY" https://api.cloudflare.com/...
However, the variable substitution is attempting to happen before the new process is spawned resulting in the value being empty and the resulting command being:
curl -sv -H X-Auth-Key: https://api.cloudflare.com/...