Additional way of configuration Keys and Ids.

[depohmel]

The current implementation of ubbagent is requiring to provide a configuration via JSON config.

Unfortunately, marketplace-k8s-app-tools default deployer is providing encodedServiceAccountKey, consumerId etc as Kubernets secrets.
K8s secrets can be mounted into Pod as File or as ENV vars. To make consumers live easy, it would nice to have another way of providing encodedServiceAccountKey and Ids into ubbagent library.
Something Keys/Secrets files path or knows ENV vars.
Similar to https://github.com/golang/oauth2/blob/ef147856a6ddbb60760db74283d2424e98c87bff/google/default.go#L43

[jvolkman]

Thanks for the suggestion. If using the metering agent as a sidecar using the provided Dockerfile, you can specify the key as an ENV var and reference the variable by name in the config. You can see an example here: https://github.com/GoogleCloudPlatform/marketplace-k8s-app-example/pull/86/files

This is all handled by the docker/ubbagent-start script, though, so if you're not using that env var support doesn't exist.

Specifically for service account keys, I think it's reasonable to support loading from files. Should be a straightforward addition.

[depohmel]

@jvolkman, unfortunately, sidecar approach didn't work. I have to use SDK one.