[OpenSIPS-Users] Change Authentication Digest URI

[AndreaM]

Hi to all,
I have to change the authentication Digest-URI value 
(http://www.opensips.org/Resources/DocsCoreVar18#toc5) before sending 
the AAA RADIUS request.
For example:

if (is_method("REGISTER"))
{
     # Change here Digest-URI (before sending RADIUS request)

     if (!aaa_www_authorize("1.2.3.4")) {
         www_challenge("1.2.3.4", "1");
     exit;
};

I tried to:
1) set $adu pseudo-variable (no way, it's a read-only PV...)
2) parse the SIP message and change Digest-URI, using "subst()" function 
from TEXTOPS module. It didn't work.
3) use "radius_send_auth()" from AAA_RADIUS module, but I'd rather not 
use it (too much complex !).

Anyone can suggest a way to change authentication Digest-URI value ?
Thank you.

AndreaM