Manual:$wgSessionProviders

Details
Specifies what providers to use for . By default,  (for normal cookie-based authentication) and   (for man>Special:MyLanguage/Manual:Bot passwords|bot passwords) are included.

Order and array keys are not relevant. By convention, the array key is the classname of the provider.

Example
or better, in PHP 5.5 and newer:

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

This will create a session provider object with  , and register it as one of the session providers. See  for details of the object construction syntax.