Manual:$wgAuthManagerAutoConfig

Extensions need to register their  implementations via this setting for AuthManager to pick it up.

Allowed values
A hash with three keys, each key a list of specifications: Beyond the usual ObjectFactory parameters, a special  parameter is also recognized; this will determine the effective order of the providers (defaults to 0; smaller first; sorting is stable). The convention is to use the provider's class name as its array key (as a convenience for site admins wanting to change it; AuthManager ignores array keys).

Example
or, if the extension uses extension registration (preferable):

This will create a pre-authentication provider object with, and register it as one of the authentication providers.