I did a cursory search and didn't see this listed.
On my CSX install, if I have .htaccess auth enabled, CSX doesn't log in any users after they're past the htaccess gateway.
1) Enable .htaccess protection on CSX dir in Apache
2) Navigate to http://[CSX directory]/[CSX path (optionally)]
3) Enter valid .htaccess username/password
4) Attempt to login to CSX with valid username/password
5) Observe that you are still "guest".
Are you using any apache modules such as mod_proxy or mod_rewrite?
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