See inline.
- I know my radius supports CHAP-MD5. Isn't it enough ?
Nope. Digest as another algorithm than CHAP that can use MD5 too
So you say I need to support Digest with MD5, or just Digest alone ?
You need to support the HTTP Digest mechanism, read the RFC.
The thing is I've using this radius for some time now, and have modified it to help my needs. I know it's a bit old already (2002). Its ic-radius and, according to its web page it does support digest.
Well, it must both support digest and the bit special way the *-digest-attritbutes are wrapped into the Digest-Attributes attribute. I don't know ic-radius. We have implemented digest for our own (commercial) RADIUS server. freeRADIUS is your best bet, or the support forum for ic-radius.
I think I'll have to implement Digest in my own radius. Any help ?
Well, not really, but freeradius has an implementation of it that you could probably look at. You need to check out the licenses though.
I do not understand how " ... the bit special way the *-digest-attritbutes are wrapped into the Digest-Attributes attribute... " is implemented. Any hint here ?
Well, if you are to implement this, you need to understand RADIUS (another RFC...). All the digest attributes are wrapped with length markers into one single attribute (Digest-Attributes). You need to read that attribute and decode it before you can use the digest attribute/value pairs for implementing Digest. g-)