[meta] Ensure module is secure

Problem/Motivation

Result of the issue is to fix flaws, ensuring module is very secure and apply for security coverage
https://www.drupal.org/docs/develop/managing-a-drupalorg-theme-module-or...

Steps to reproduce

Proposed resolution

Remaining tasks

• Registered users have access to content they should not access to: #3384410: [meta] Improve access control
• Probably strings processing is not in robust secure state, so this has to be thoroughly reviewed. #3388695: Sanitize strings properly [complete]
• Read all the documentation about security coverage to sort out a detailed plan to get it.

User interface changes

API changes

Data model changes