Manual:$wgCookieDomain/ja

詳細
ログイン Cookie のドメインを明示するために設定します. 例: 、またはサブドメインすべての場合は

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.