i have this in asterisk integration how to, and i noted the "exit" before the "if($au!=$tU)" .. i dont understan the conditional and the exit there!
please can someon xplain me that!?
# authenticate the REGISTER requests (uncomment to enable auth) #!ifdef WITH_ASTERISK if (!www_authorize("$td", "sipusers")) #!else if (!www_authorize("$td", "subscriber")) #!endif { www_challenge("$td", "0"); exit; } if ($au!=$tU) { sl_send_reply("403","Forbidden auth ID"); exit; }
i investigate at the kamailio cgf documentation and there's no clear topic related!
http://www.kamailio.org/wiki/cookbooks/5.2.x/pseudovariables#tu_-_to_uri
Lenz McKAY Gerardo (PICCORO) http://qgqlochekone.blogspot.com
Hi,
When any SIP request arrives at the proxy, it asserts some kind of identity ("I am claiming to be sip:alex@sip.evaristesys.com").
In most SIP requests, this is the From URI ($fu) identity, but in REGISTERs, it's the To URI ($tu), because according to the standard, the AoR (Address of Record) that the registration seeks to establish a binding for is situated in the To URI.
This identity can be trusted at face value, but usually isn't; that's the reason for the RFC 2617-inspired digest challenge / authentication mechanism. The proxy sends a nonce (temporary encryption key of sorts) and expects a new request which has an additional header (e.g. "Authorization") whose value is encrypted with that nonce. This Authorization header has several parameters, one of which is an "authentication username" -- exposed in the Kamailio config as $au.
The check you are asking about ensures alignment between the authentication username and the broader "identity" username, if you like. This is usually desirable, because otherwise, I could register with an AoR of "sip:lenz@sip.evaristesys.com" as long as I have some other, valid credentials on the system. In other words, I could use my username for 'alex' in order to establish a registration of "sip:lenz@sip.evaristesys.com". But if alignment betweeen $tU == $au is assured, then I can only use authentication credentials for 'alex' in order to register an identity of 'alex', and you can only use authentication credentials for 'lenz' to bind an identity of 'lenz'.
Does that make sense?
-- Alex
On Tue, Oct 29, 2019 at 11:35:45AM -0400, PICCORO McKAY Lenz wrote:
A savvy colleague reminded me to add that there are, occasionally, valid reasons to relax this authentication vs identity concordance policy.
The main one comes up in Class 4/trunking environments, such as the kinds we deal with as our bread and butter. In this universe, a lot of caller ID/calling party name information is signalled in INVITEs using the From header, without necessarily the option of superseding that with P-Asserted-Identity or Remote-Party-ID (obsolete draft but stubbornly in use). Moreover, the calling party information sent can vary depending on which endpoint is making the call, so it is not practical to make it align with a single set of digest authentication credentials for the trunk.
For example, a customer may wish to send an outbound caller ID of:
From: sip:+14045551212@sip.evaristesys.com
along with a dozen other possible numbers.
And the From URI may be their only viable means of sending it, as a matter of technical limitations or policy. But their authentication credentials would be a username or an account ID or something like that, so sending them a 407 Proxy Authorization Required challenge with the expectation that their response have an $au that aligns with their $fU is not realistic.
So, on some installations, it is either necessary or expedient not to enforce this requirement and just hope for the best.
For this reason, almost all the Kamailio auth functions provide flexibility to turn this more draconian enforcement or on off. For example, the auth_check() function in auth_db has a 'flags' parameter:
https://kamailio.org/docs/modules/5.3.x/modules/auth_db.html#auth_db.f.auth_...
From the above documentation, flag 1 is:
"If it is 1, then the function will check to see if the authentication username matches either To or From header username. REGISTER requests: From and To must match the authentication user."
This flexibility is a nod to the reality that this policy is not always appropriate or practical.
-- Alex
On Tue, Oct 29, 2019 at 01:18:27PM -0400, Alex Balashov wrote:
Gorgeous explanations!
On Tue, Oct 29, 2019 at 6:36 PM Alex Balashov abalashov@evaristesys.com wrote:
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Alex Balashov -
Giovanni Maruzzelli -
PICCORO McKAY Lenz