Support loading parameters from environment variables

[leipert]

Summary

It seems like click supports loading parameters from env variables. This would make it easier to:

1. Configure a docker container in docker-compose with env variables
2. Potentially be a little more secure, because providing --password currently prints the password in certain contexts (e.g. ps)

Context

Found my password exposed in the ps tree in the portainer interface.

[choval]

You could pipe the password to icloudpd.

I have a shell script that I set as the entrypoint for the docker image.

#!/bin/sh
echo $PASSWD | /app/icloudpd_ex icloudpd ...

But I agree, if we could use an environment variable for it, it would be much better.