[Serusers] SER, Radius and /etc/passwd

Hi All, I'm trying to implement SER into an existing system, and having problems with radius authentication. RTFM and lots of google hasnt helped! The existing working freeradius server uses Unix (/etc/passwd) file (on FreeBSD) to authenticate users who dial into a modem server. I'd like to use the same accounts and passwords for SIP users, using the same radius server. I'm using the default modparam values for module auth_radius. However, the doco suggests to me that I have to use Digest authentication when I call radius_www_authorize. But the cleartext password is not available to the Radius server(ie I'm not using entries in the radius "users" file) so I cant see how it could do Digest authentication at its end. The existing authentication uses Auth Type := System. So, can I get SER to do cleartext auth to the radius server (both are on the same, isolated subnet, so I'm not worried about traffic being captured) Is there a service_type or something else? Any advice appreciated Steve