I need to write a nginx module to enhance the performance of our service.The following is what our service doing,

1. When getting the http request from the client, our service send http request to another server to validate the identification of the client.

2. If the validation passed, then send http request to another server to get the metainfo of the file requested by the client.

3. If the metainfo is retrieved, use the metainfo to pull file data from backend stroage using http GET.

I've read the guide of nginx module developement, but that's not enough, these days, I've been reading the code of nginx. It's a hard job, i confess.
I think, I should write a handler module, and using upstream to interact with other services, as far as i know , upstream send the response directly to the client, the only thing I can do is defining an "input_filter" of upstream, I'm wondering whether "input_filter" can be used to initiate another upstream request.

Any one can help ? Thanks in advance!