WP8 Uploading/Downloading large files

WP8 Uploading/Downloading large files

I am fairly new to Windows Phone development. We have a scenario where we
allow user to upload or download files but along with authentication
(oAuth, NTLM, forms all standard mechanism but not limited to oAuth).
Those files are uploaded to SharePoint.
Now so far our RnD suggest that we have following options
1- Resource Intensive Agent The constraints associated with Resource
Intensive (like Minimum battery etc.) have lead us to drop this option
2- Periodic Agent A relatively better option, however as they run after 30
minutes and the constraint of 10 minutes duration gives us doubt that on
mobile if user wants to upload a video of say 1-2 GB, it does not
guarantee competition and u can anticipate other problems associated with
this approach.
3- Background File Transfer This is the best option in our scenario
however my colleague told me that it does not support basic windows
authentication and that we cannot change user-agent etc.
4- On Application Another option is to perform network operation on
application but we cant retain user on application for longer duration and
also after sometime lock screen would appear. So...
Can anyone who have experienced similar scenario or from product team can
guide here. It's a common scenario, are we missing something here? or is
it really API limitation?