Nginx auth_basic and rewrite in subdirectory does not work - nginx

Question

I'm trying to add a project to a subfolder of existing webserver with Nginx. Here's my simple config:
server {
listen 80 default_server;
server_name localhost;
root /var/www;
[...]
location = /my-project { return 301 /my-project/; }
location /my-project/ {
alias /var/www/my-project/web/;
index index.php;
location ~ /[^/]+/control(/|$) {
auth_basic "Restricted";
auth_basic_user_file /etc/nginx/htpasswd;
if (-f $request_filename) { break; }
rewrite ^(.*)$ /my-project/index.php last;
}
if (-f $request_filename) { break; }
rewrite ^ /my-project/index.php last;
location ~ ^/[^/]+/index\.php$ {
include fastcgi_params;
fastcgi_pass unix:/var/run/fcgi.sock;
fastcgi_param SCRIPT_FILENAME $document_root/index.php;
}
}
}
Because there is an rewrite directive inside /control location block, the auth_basic never gets triggered, because Nginx executes rewrites before authentication. In which way should I modify the config, that auth does work?
PS: try_files doesn't seem to work, because it serves files from root (/) webfolder!? When I replace the if and following rewrite with try_files $uri /my-project/index.php?$query_string; I get a 404, because Nginx tries to serve the file /var/wwwindex.php (have a look at missing slash and the root folder /var/www instead of alias).
EDIT 18.09.2013:
As VBart suggests I'm using now the following configuration to get authentication to work
location ~ ^/(?<dir>my-project)(?<path>/.*)$ {
root /var/www/$dir/web;
location ~ ^/[^/]+/control(/|$) {
auth_basic "Restricted";
auth_basic_user_file /etc/nginx/htpasswd;
try_files $path /$dir/index.php?$query_string;
}
try_files $path /$dir/index.php?$query_string;
location ~ ^/[^/]+/index\.php$ {
include fastcgi_params;
fastcgi_pass unix:/var/run/fcgi.sock;
fastcgi_param SCRIPT_FILENAME $document_root/index.php;
}
}

Answer 1

Use:
error_page 404 =200 /my-project/index.php;
instead of ugly rewrites:
if (-f $request_filename) { break; }
rewrite ^(.*)$ /my-project/index.php last;
Reference:
http://nginx.org/r/error_page
http://wiki.nginx.org/IfIsEvil
http://wiki.nginx.org/Pitfalls
P.S. try_files doesn't work with alias because of bug: http://trac.nginx.org/nginx/ticket/97, but you can replace alias with root directive: http://nginx.org/r/root