When I try logging in my vbulletin forum via www, it will still show me as logged out.

But when I type the url without the www, I will be logged in as per normal.

Any idea how to fix this so that when user open up the site via www or without www, they won't encounter this issue?

If I use .htaccess redirect, how do I add it to mine bearing in mine I have vBseo installed in my forum?

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC]
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]