Sorry for this noob question, but frustration is eating me.
I'm trying to set up my php app for 2 straight days, and no config seems to work to load it properly.

My config:

server {
server_name mydomain.com;
...
...

fastcgi_param HTTPS on;

location /app {
index index.php;
alias /var/www/app;

location ~ \.php$ {
try_files $uri =404;
include /etc/nginx/fastcgi_params;
include /etc/nginx/fastcgi.conf;

fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_pass unix:/var/run/nginx/php-fastcgi.sock;
}
}
}

But I also tried a number of other placement and combinations.

This will result (probably obviously) in a "No input file specified."
SCRIPT_FILENAME will never be taken unless I change it explicitly to /var/www/app/index.php (and in that case only that file loads, 404ing all other php files out).

What could be the issue? Where could I even debug this? (in terms of what file nginx is trying to feed php-fpm)