Configuration pb: incorrect redirection when authenticating

Hi, I'm new to XWiki. I've configured it behind Apache (XWiki is running on the same host and listening on tcp/7070). Apache uses a simple RewriteRule to send all trafic to XWiki. That works fine, except when I change the Xwiki configuration to request authentication of all visitors. In this case, the (unauthenticated) visitor is redirected to: http://localhost:7070/xwiki/bin/login/XWiki/XWikiLogin;jsessionid=22... instead of http://mywiki.fr/xwiki/bin/login/XWiki/XWikiLogin... The same thing occurs when my administrator session expires, but the all other links (including "Log-In) work. Seems to me like a bug or misconfiguration. Any idea ? Thanks for your help Emmanuel