Hide sensitive data in docker compose

[felipeleon73]

Actual Result / Problem

There seems to be no way to hide sensitive data in docker-compose using mysql as storage. In particular, in the connection string the password appears unencrypted.

Expected Result / Suggestion

It would be useful to be able to use a file from which to read the mysql password and put it in an environment variable (for example SSHPORTAL_DATABASE_PASSWORD_FILE), or at least all the connection string (SSHPORTAL_DATABASE_URL_FILE), thus making it possible to use docker swarm secrets.