Drupal
The enterprise OpenSource content management system which is available for free at https://www.drupal.org where you can find all the details and also references.
Drupal has a very active community with tens of thousands of developers all around the world and they also have a huge focus on standard compliance and on security.
The User hash module allows you to create an individual hash for each user. Use it as a light-weight user identification where you do not want to use the Drupal login credentials. E.g. as an individual API Key for reading insensitive content.