Processing Web UI upload requests through a Rails Proxy Application

Hello,

I'm trying to do some work to capture and analyze requests on the app.box.com Web UI through a Rails/Rack proxy application. At this point, I have a squid proxy relaying requests for *.box.com and *.boxcloud.com through my Rack application and I am simply relaying those requests to upstream box sites.

Everything seems to work at this point, with one exception. The upload through the Web UI gives me the "There was an error with your upload, please try again." message. I've walked through the underlying code and it seems that it has something to do with the response from the upload_session_id JSON response not validating properly, although I have not stepped through the JS application to verify this.

Any thoughts on what validation I may be tripping up when trying to put my Rack proxy in the middle of this?