Manual:$wgCookieDomain/zh

细节
Set to an explicit domain on the login cookies, e.g.  or   for all your subdomains.

如果默认的Cookie作用域没有设置，那么PHP中的 函数会将Cookie的作用域设为当前域. 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.