Consider improving SYNAPSE_ENABLE_REGISTRATION handling in docker

[pkoziol]

Description

Recently I discovered that my server allowed people to register. It turns out that setting in docker-compose.yml:

- SYNAPSE_ENABLE_REGISTRATION=no

doesn't disable registration. You have to remove variable completly.

I know (now) that contrib/docker/README.md says to set this variable to enable registration, so one may guess that you should unset variable to disable registration.

I'm not that smart apparently.

Version information

• Homeserver: my private homeserver
• Version: 0.31.1
• Install method: docker-compose
• Platform: docker

[turt2live]

This also tripped me up a couple times. Falsey words should be falsey imo

[hawkowl]

As per #5518 , we're going to remove support for the environment variable method of configuration, which will fix this bug by making it more explicit what the configuration is.