[Serusers] Can SER digest-authenticate itself to PSTN servers when forwarding requests from clients?

Hi all, I'm new to SER, so maybe the question is trivial. What I'm wondering if there's a way SER can itself (!) authenticate using digest authentication on a PSTN gateway? Obviously I can't use "rewriteuserpass" because this doesn't support digest authentication. Background: I'm using a hardware SIPphone (BT100) that can only connect to one single SIP server. I'd like to make it connect to SER running on my Linux box. SER would not need to authenticate the phone itself (it's my private LAN segment anyway). SER should register itself (not the phone) as a UA to several SIP servers in the Internet on behalf of the BT100 (like Stanaphone, Sipgate, Nikotel, etc). To do so, my credentials for these servers are placed on the Linux box (in cleartext). Of course these servers require digest authentication, jence my initial question. As soon as I make a call on teh BT100, SER can use a dialing plan in order to decide what PSTN to connect it to - but this should be invisible to the BT100, the SER proxy should even take care itself of the digest authentication. I browsed the auth module - but I can only find actions in there that would allow the proxy to digest-authenticate incoming requests - or did I miss something? I don't really feel like installing a MySQL server either (for my 2-3 accounts), unless really needed. What I need though is a way how the proxy could itself - independent of the calling client - authenticate on different servers (using different credentials at each server). Is this possible using SER? Or maybe some other software? Thanks, Andy