saving binary POST data to disk

Hello,

I'm working on a Microsoft Office Online integration, and they POST data
to us (we use nginx in a rails app), but the post body is binary data,
not multipart/form-data.

I'd love to use nginx-upload-module, or something similar to save the
binary data to disk, then pass the request to rails. Is anyone aware of
any other nginx modules that would do this? I tried
nginx-upload-module but I get
NGX_HTTP_UNSUPPORTED_MEDIA_TYPE because there's no Content-Disposition
header coming through the POST.