ngx_http_secure_download report back to application?

[Pascal Nitsche]

Hello,

I'm thinking about writing an application, which should use nginx' 
secure download module to generate secure - expireing - links and limit 
the number of (successful) downloads. Since it only should count 
successful downloads it needs to know if the download was successful so 
it would be good to have nginx report to the application "Hey, I've got 
one more complete download". In the best case also "Download failed, but 
I transfered N bytes" for statistical reasons inside the application 
(This could be used to track traffic usage by file and stop generating 
links if a traffic limit has passed).

The download server and the application server could - but haven't to - 
run on different machines.

Now my question is: Is something like this possible? Can I send a 
response to an application in - let's say XML or JSON? And if yes: How?

Thanks in advance,

Pascal Nitsche