Manual:Hooks/UserEffectiveGroups

Use cases
The  hook lets MediaWiki installations filter and add to the list of user groups stored in the MediaWiki database. For example, one might wish to synchronize the user groups with the host operating system or with a third party package.

Usage
At the time of invocation  is populated with the groups assigned to the user by the User groups table. Functions attached to this hook change the groups by adding or removing array elements.