Hello MohaBeacon,
can you try to disable HTTP auth with the following commands ?
# make a backup of acl.conf
cp /etc/nginx/common/acl.conf /etc/nginx/common/acl.conf.bak
# make acl.conf empty
echo '' > /etc/nginx/common/acl.conf
# reload nginx
service nginx reload
Let me know if you are still unable to access backend.