I have successfully configured a .htaccess and made it work. The following is a sample for the rewrite result:
A: user.sitename.com/blog
will be mapped to:
B: http://www.sitename.com/modules/blog/index.php?username=user

Yes, as many of you can image, when I logged to this site (http://www.sitename.com) and click a URL such as A, the expected page will be loaded, together with the problem, that is, the logged status was changed, $xoopsUser was changed to NULL. My question is how to keep the logged status as the right user when I use the URL such as A which is mentioned above. Millions Millions thanks ahead！

Cookies, which store authentiication information, are domain-based... As I see - you change host's domain, thus - old authentification ignored for new hostname.
I have almost the same problem in case of multisiting with common userbase, and have only ideas how it can be solved (by dirty hack), not ready to use solution

Hi LazyBadger,

Thanks for your 'only ideas', by following your ideas I successfully have this problem sorted!!!! Thank you very much!!

The solution:
I just set session.cookie_domain param to my domain as ".mydomain.com", so that the cookie's scope expand to all subdomains (the default is only in http://www.mydomain.com). Fairly easy hah?

Quote:
Don't mention... It's my last thing here - I was consideed too bad and dangerous by some persons and was banned today from XOOPS sites - and I move into "deep lurk mode"