I want to redirect all calls to http://mydomain.com/index.php to http://mydomain.com to avoid duplicate pages.I use this
if ($request_uri ~* "^/index.php\??$") {
rewrite ^.*$ http://$host? permanent;
}

but it doesn't seem to work properly. Although it redirects I cannot login or logout anymore in Joomla, it simply redirect to homepage without login or logout. What am i missing here ? How do i do this properly ? Of course if i remove that everything i fine, it works for example for home.html but not for index.php.
Thank you.