[OpenSIPS-Users] learning the realm from authentication challenges

Fri Sep 25 14:57:10 EST 2020

Gotcha. I was missing the part where you want to accept any realm and don’t want to know the realm ahead of time. Interesting case. Thanks for explaining.

Ben Newlin

From: Users <users-bounces at lists.opensips.org>
Date: Friday, September 25, 2020 at 10:41 AM
To: OpenSIPS users mailling list <users at lists.opensips.org>
Subject: Re: [OpenSIPS-Users] learning the realm from authentication challenges
I am not route-advancing in a typical way, so my application of credentials is a bit different perhaps.

The environment I'm in has a variety of customer-facing platforms, over a dozen at last count.  Some are for trunking, some hosted, some hybrid.  The platform I'm writing on OpenSIPS is a testing one that will allow us to send and receive test calls to and from all of them.  So, rather than having a bunch of registrations on every test phone for every person who might want to test, this allows each person to have one appearance to this platform and select which upstream platform they want to send a call to via dialed prefixes.

I use the uac_registrant module, and its registrant table, to handle the platforms that require registrations and it works excellently.  At call time, I'm working on the scripting right now that will query the registrant table for the appropriate credentials based on where we've sent the call and apply them in the failure_route upon receiving a 401 or 407.

Think of it this way:  when you configure a gateway in FreeSWITCH or a SIP peer in Asterisk's chan_sip, do you need to define the realm ahead of time?  No, you don't care; it's just a mechanism under the hood that's necessary to complete the transaction.  That's where I'm at in OpenSIPS.  With Johan's parsing it looks like I'm about there, too.  Friggin' regex gets me every time.

- Jeff

On Fri, Sep 25, 2020 at 10:25 AM Ben Newlin <Ben.Newlin at genesys.com<mailto:Ben.Newlin at genesys.com>> wrote:
I think you do need to have credentials associated with the different routes you have and load those properly. From your description, however, I don’t understand why it is dependent on identifying the realm in the response. If multiple downstream servers are all using the same realm (but have different credentials?) then how are you differentiating based on the realm value?

The idea with uac_auth is that when you send, for example, to server broadworks1 you would load all the possible valid credentials for broadworks1, including the realm it will challenge with. When you then call uac_auth() from failure route, it will look through all the loaded credentials for one with a matching realm to the broadworks1 challenge and use that. If the call fails for any reason to broadworks1 and then you decide to route to server asterisk1, you would load all the possible credentials for that server into the auth AVPs the same way and failure route handling is the same.

You could very well have a use case for verifying the realm in failure_route; I’m not saying you don’t. I don’t see it from what you’ve described, but I may be missing something. I think the reason there is no variable for pulling the challenge realm value directly is because normally with this mechanism it shouldn’t be needed.

I would appreciate if someone could confirm that uac_auth() will match the realm as I’m asserting. I’m 95% sure this is how it worked in my testing, but that was a while ago and as I said the realm matching doesn’t appear to be documented. I’d hate to be steering you down a wrong path.

Ben Newlin

From: Users <users-bounces at lists.opensips.org<mailto:users-bounces at lists.opensips.org>>
Date: Friday, September 25, 2020 at 10:15 AM
To: OpenSIPS users mailling list <users at lists.opensips.org<mailto:users at lists.opensips.org>>
Subject: Re: [OpenSIPS-Users] learning the realm from authentication challenges
Johan,
  I will definitely try that.  Thank you!

Ben,
  The problem is I have multiple destinations with the same realm.  In my case, several different Broadworks app servers.  I haven't checked them exhaustively but I think they all reply with realm="BroadWorks" in their authentication headers.  I've got some Asterisk boxes in here, and I think they're all the domain of the SIP request URI in the case of an INVITE.  I think I'll have to choose ahead of time which credentials go with which route, no?  Unless I'm still not wrapping my head around how this is supposed to work.

- Jeff

On Fri, Sep 25, 2020 at 9:22 AM Ben Newlin <Ben.Newlin at genesys.com<mailto:Ben.Newlin at genesys.com>> wrote:
Jeff,

My point was that the uac_auth() is supposed to handle the realm matching for you. If you simply load all of the auth data based on the call target as you already plan to do, uac_auth() should look through that data for you to find credentials with a matching realm. You don’t need to do that part yourself in the script.

Ben Newlin

From: Users <users-bounces at lists.opensips.org<mailto:users-bounces at lists.opensips.org>>
Date: Thursday, September 24, 2020 at 11:14 PM
To: OpenSIPS users mailling list <users at lists.opensips.org<mailto:users at lists.opensips.org>>
Subject: Re: [OpenSIPS-Users] learning the realm from authentication challenges
Good catch on Proxy-Authorization vs Proxy-Authenticate.  I think I've been looking at this too long.  I checked the module and that's exactly what it is.

My hope was to load the uac_auth user/pass AVPs ahead of time from a DB based on where I knew I was sending the call, load the realm one in the failure route based on what comes back in the header, and then fire the uac_auth() function.  It looks like I may have to manually extract the realm from whichever header comes in.  Not ideal, but probably workable.

- Jeff

On Thu, Sep 24, 2020 at 9:58 PM Ben Newlin <Ben.Newlin at genesys.com<mailto:Ben.Newlin at genesys.com>> wrote:
This does not appear to be documented, but I believe uac_auth() looks through the AVPs configured in the UAC_AUTH module and uses the first one whose realm matches the challenge realm. So in order to authenticate any challenge, you must load all of the possible credentials into those AVPs.

Ben Newlin

From: Users <users-bounces at lists.opensips.org<mailto:users-bounces at lists.opensips.org>>
Date: Thursday, September 24, 2020 at 9:53 PM
To: OpenSIPS users mailling list <users at lists.opensips.org<mailto:users at lists.opensips.org>>
Subject: Re: [OpenSIPS-Users] learning the realm from authentication challenges
According to the docs, $ar provides the realm from the “Authorization” or “Proxy-Authorization” headers. Not from the ”Proxy-Authenticate” header, which is what you have.

https://www.opensips.org/Documentation/Script-CoreVar-3-1#toc6<https://www.opensips.org/Documentation/Script-CoreVar-3-1#toc6>

Ben Newlin

From: Users <users-bounces at lists.opensips.org<mailto:users-bounces at lists.opensips.org>>
Date: Thursday, September 24, 2020 at 9:31 PM
To: OpenSIPS users mailling list <users at lists.opensips.org<mailto:users at lists.opensips.org>>
Subject: [OpenSIPS-Users] learning the realm from authentication challenges
I'm trying to recover the realm of an auth challenge to OpenSIPS so I can respond to it with the uac_auth() function, and that requires knowing the realm.  The docs say that $ar<https://www.opensips.org/Documentation/Script-CoreVar-3-1#toc6> should provide that, perhaps written like $(<reply>ar) to get it in the right context.  I'm having some trouble getting the data.

failure_route[relay_failure] {
...
        if (t_check_status("407")) {
                xlog("L_NOTICE", "[1] Proxy-Authenticate: $(<reply>hdr(Proxy-Authenticate))\n");
                xlog("L_NOTICE", "[2] Auth Realm: $(<reply>ar)\n");
                xlog("L_NOTICE", "[3] Auth Realm: $ar\n");
        }
...
}

The logs show:

/usr/sbin/opensips[33044]: [1] Proxy-Authenticate: Digest realm="asterisk", nonce="5f6d42140000936ad820dbcd452e6bcd145777e458dd46dd", qop="auth"
/usr/sbin/opensips[33044]: [2] Auth Realm reply: <null>
/usr/sbin/opensips[33044]: [3] Auth Realm: <null>

Is it possible to get the realm?  Is it possible to build a response with uac_auth() for an arbitrary authentication challenge?

This is on 3.1.0~20200923~88f89e941.

- Jeff

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