Properly Configure Nginx alias directive with PHP

When using alias directive, the SCRIPT_FILENAME parameter passed onto FastCGI interpreter should be $request_filename instead of the default $fastcgi_script_name. This ensures that the PHP interpreter receives the correct file path and does not return 404 Not Found.

Example Code:

   location /myalias {
      alias /path/to/alias;
      location ~ \.php$ {
         fastcgi_pass fastcgi_backend;
         include fastcgi_params;
         fastcgi_param SCRIPT_FILENAME $request_filename;
      }
   }