Rewrite within location with a new root/alias - Nginx - nginx

Question

My folder structure is as follows:
/www
/api.domain.tld
/app.domain.tld
The API contains the system it self and APP implements the API via HTTP.
I want to create an Nginx server for app.domain.tld that also contains an "virtual directory" for API.
You can contact the API likes this: http://api.domain.tld/method/api.json
But it would be great if the API can be contacted like this also: http://app.domain.tld/api/method/api.json without copying something into APP, but keep those two "systems" separated.
What I have for now:
server {
listen 80;
root /var/www/app.domain.tld;
index index.php index.html;
server_name app.domain.tld;
location ^~ /api {
alias /var/www/api.domain.tld;
location ~ \.php$ {
try_files $uri = 404;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}
rewrite ^/api/([a-z]+)/api.json$ /api.php?method=$1 last;
}
location....
location....
location....
location ~ \.php$ {
try_files $uri = 404;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
}
}
Unfortunately this does now works as expected.
The rewrite does not work at all. I can get api.domain.tld/index.php but when it needs to use the rewrite, it will not work.
I have tried several things. Either I get 404 or 403 with this error:
directory index of [path] is forbidden
Can someone come up with a better solution that actually works?
Regards

Answer 1

You should change SCRIPT_FILENAME path:
server {
listen 80;
root /var/www/app.domain.tld;
index index.php index.html;
location ~ ^/api/(.+\.php)$ {
alias /www/api.domain.tld/public/$1;
fastcgi_pass 127.0.0.1:9000;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $request_filename;
include fastcgi_params;
}
}