[Users] Cisco authentication

Hi all, I've a working openser and a cisco router (17xx). I'd like to authenticate the cisco router as a sip ua. If I disable www_authorize everything is working fine and the router register to the server. If I enable it and configure the router with

sip-ua authentication username xxx password xxx realm xxx

I see the router trying to register, but no way to make it working. I tried I think every combination of realm in www_authorize, www_challenge and so on.

If I debug a successful authentication, I see a query on the db, "select ... from subscriber". If I debug the cisco auth, the server doesn't even try the query.

Has somebody any hint please?

TIA,