Update security guide

To be checked and to be updated upon next release
- the difference in the authorization for non-prod and prod environments
- the difference in headless and headful application
- the difference in development mode and published mode

cc @meryllblanchet

Start by locating the security guide referenced in the issue and review its current authorization, headless/headful, and development/published-mode sections. Check the next release context before editing; done means all three environment or mode differences are accurately documented for that release.

Written by the indexing model from the issue text.