allow Docker Secrets (eg; for db password)

[Slevin90]

Prerequisites

• [ OK] I have searched open and closed issues to make sure that the bug has not yet been reported.

Bug report

the database password is visible in config > .env file
in the DB_URI -variable

Expected behavior
A safe method would be to use different variables (db_username, db_password, db_name) with support Docker Secrets
same for other secrets that can be used in the config

also makes a cleaner conmpose-file where the password can be re-used in the postgres and simplelogin config

[Slevin90]

simple-login/simplelogin-postfix-docker#9

similar as the simplelogin-postfix-docker did already

[Blizzke]

Even without secrets (which is swarm only and IMHO extremely unusable if you rotate secrets) and *_FILE support I would still never add passwords to the docker-compose file (which you usually want in you git repository. I just use env_file.

docker-compose.yml:

services:
  test:
    image: busybox:latest
    env_file:
      - .env

.env:

TEST_PASSWORD=password

docker compose config:

name: tmp
services:
  test:
    environment:
      TEST_PASSWORD: password
    image: busybox:latest
    networks:
      default: null
networks:
  default:
    name: tmp_default

The .env is just included in the folder where the stack sits but not included into your versioning system (they are usually part of the default .gitignore