Manual:$wgCookieDomain/fr

Détails
Définir un domaine explicite sur les cookies de connexion, par ex. ou  pour tous vos sous-domaines.

By default this isn't set, so php's  function will just set a cookie on the current domain. This is a bad thing if e.g. your site is available from both  and , since users that log into the former will be logged out as soon as they visit the latter.