There was a bug in nginx-auth-pam module, it should be fixed with this patch:
http://anonscm.debian.org/gitweb/?p=collab-maint/nginx.git;a=commitdiff;h=bdf157e88 -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org