One of the sites that I’ve been working on recently for some odd reason would not log users in (or at least not constantly). After looking into it further, I realized it had to do with the PHP function “header” redirecting the user if the login query was successfully.

The problem came when a user came to the site without typing in “www”. The page was redirecting to the site WITH the “www” and the $_SESSION vars were not getting set.

So to force every page to include the “www”, I added the following 3 lines to the .htaccess file and everything seems to be working fine.

RewriteEngine on
RewriteCond %{HTTP_HOST} !^www.domain.com$
RewriteRule ^(.*)$ http://www.domain.com/$1 [R=301]