Re: [tram] Oauth vs Origin [Was: Path Forward for STUN ORIGIN]

[Brandon Williams <[e-mail]>]

I agree that using the RFC7635 mechanism can work for #2, and I prefer 
that to ORIGIN for this purpose. That said, I think the mechanism is 
currently underspecified, in that there is nothing explicitly defined in 
RFC7635 that could be used to play the role of ORIGIN for auth purposes, 
so interoperability could be an issue.


If the kid value delivered in the USERNAME attribute is unique to the 
relay, then the kid value alone is enough to allow ORIGIN 
identification. This rules out the method for key distribution describe 
in section 4.1.1 of the RFC though, since that method has the auth 
server selecting the keys/kid, not the relay server, and I don't know 
how the necessary uniqueness would be guaranteed in that case. As long 
as the kid is unique to the relay, though, the necessary keys can be 
retrieved.


If the kid is not guaranteed to be unique for the relay, then some 
method to qualify the kid and provide uniqueness would be necessary. 
Either ORIGIN or REALM could be used for this purpose, but whichever one 
it is would itself have to be unique for the relay in order to ensure 
that qualifier+kid is unique.


RFC7635 doesn't impose requirements on kid uniqueness, nor does it 
require REALM, ORIGIN, or any other source of uniqueness to be present 
in the message that contains the token. Provided that either kid or 
realm+kid is unique to the relay, I agree that ORIGIN itself is not 
required for auth and the information could be delivered via some other 
mechanism.


All of this assumes that the STUN server name sent to the client from 
the relay as part of the initial unauthenticated exchange is a global 
value for the service and does not need to be allowed to be ORIGIN 
specific. In other words, any OAuth server that generates an access 
token for the 3rd party relay service would receive the same server name 
from a specific STUN server.


--Brandon


------------------------------------------------------------------------
*From:* Justin Uberti <[e-mail]>
*Sent:* Wednesday, August 26, 2015 7:08 PM
*To:* Alan Johnston
*Cc:* [e-mail]; [e-mail]
*Subject:* [tram] Oauth vs Origin [Was: Path Forward for STUN ORIGIN]
splitting thread

On Wed, Aug 26, 2015 at 2:07 PM Alan Johnston <[e-mail] 
<mailto:[e-mail]>> wrote:

    Justin,

    It is an important question for the WG on whether ORIGIN is a useful
    solution to the use cases. Hopefully we'll get more feedback on this.

    Your comments seem mainly directed towards a solution for use case
    #2 below (REALM selection for TURN authentication), right?  I'm not
    sure if use case #3 applies or not.  I don't think OAuth helps with
    #1 or #4 or #5.


I think OAuth can solve #1, #2, and #3. The app's interaction with the 
AS can give the AS context, which can be encoded into the returned 
token. This then allows the TURN server to have this context when 
receiving the token, such that it can make informed decisions for #1/#2/#3.


    I know we have discussed it before, but I also don't think that
    everyone believes that OAuth means that ORIGIN is no longer needed.
    There have been suggestions that a multi-tenanted TURN server using
    OAuth might still use ORIGIN.


Since the origin can be determined by the AS, it's not clear why this 
would also be needed at the TURN server. One might ask, why it is better 
to use origin to the AS versus the TURN server? The upsides of origin 
over HTTP to AS are that 1) it is encrypted and 2) it's easier to deal 
with the privacy implications of origin in a single protocol rather than 
2 protocols.


    And using domain-specific USERNAME attributes sounds a bit like the
    problem that Martin mentioned of simply working around the approach.

Yes - that's what I was trying to say as well.

    - Alan -

    On Tue, Aug 25, 2015 at 3:50 PM, Justin Uberti <[e-mail]
    <mailto:[e-mail]>> wrote:

        Overall, I think most/all of the goals that ORIGIN is trying to
        accomplish would be better handled by STUN OAuth
        (https://datatracker.ietf.org/doc/draft-ietf-tram-turn-third-party-authz/
        <https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-2Dtram-2Dturn-2Dthird-2Dparty-2Dauthz_&d=BQMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bwZ-nnRGWmcGKRIuadq6-NSnsgwbBVUJa4mZfmEIBXg&m=YAVYqLAvlnjV5WFeb0DMhGTziYu4jLvpB3UTCbrR8T4&s=uYVEJtj6D0D8AALXY1GfSzY-RO-q9CHJJjr2mCjvWlk&e=>)


        Generally, it's not clear that ORIGIN is a great solution for
        any of the use cases listed.
        1) is easily accomplished via oauth, without any of the
        restrictions present here
        2) can be dealt with using other means (e.g. oauth, or supplying
        domain info in USERNAME)
        3) is fairly weak control, and can be done better through oauth,
        or domained USERNAMEs

        Of course, as noted by others, use of domained USERNAMEs creates
        a quasi-ORIGIN value within the USERNAME attribute, which makes
        OAuth more attractive.

        On Tue, Aug 25, 2015 at 12:57 PM Alan Johnston
        <[e-mail] <mailto:[e-mail]>>
        wrote:

            All,

            Based on feedback during IETF-93 in Prague, the authors of
            draft-ietf-stun-origin are looking for feedback on a
            possible path forward to solve the privacy/meta data issues
            and clear the DISCUSSes (see
            https://datatracker.ietf.org/doc/draft-ietf-tram-stun-origin/ballot/
            <https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-2Dtram-2Dstun-2Dorigin_ballot_&d=BQMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bwZ-nnRGWmcGKRIuadq6-NSnsgwbBVUJa4mZfmEIBXg&m=YAVYqLAvlnjV5WFeb0DMhGTziYu4jLvpB3UTCbrR8T4&s=lx5ApLOv-KiXbtLZppLxrkE5vHcqXhUqPSXlDcF-O28&e=>).
            There are two areas of feedback: Use Cases and Proposed
            Solution.

            Use Cases
            ========

            First, we want to be sure that we are considering all the
            use cases for STUN ORIGIN.  In the draft, three are described:

            1.  Logging of usage of STUN/TURN server. An operator of a
            STUN or TURN server would learn the Origin of the web, SIP,
            and XMPP users.

            2.  REALM selection for multi-tenanted TURN server. This
            avoids having to run multiple instances on different ports
            or IP addresses when more than one REALM is in use.

            3.  Service determination after authentication.  Bandwidth
            or QoS policy can be applied, after authentication, based on
            the Origin.

            Also, the following use cases have also been discussed but
            are not in the draft

            4.  Authorization at border TURN server after
            authentication.  An enterprise border TURN server can apply
            policy and allow usage for certain Origins (whitelist) or
            block usage of others (blacklist).

            5. draft-jennings-behave-rtcweb-firewall-01 discusses how a
            firewall with STUN server could use ORIGIN in authorization
            decisions.

            Are there any other use cases we should consider?

            Possible Solution
            =============

            The solution that was discussed in Prague that seems to be
            the best tradeoff between privacy and functionality is to
            only include ORIGIN information in a STUN or TURN request if
            the domain of the Origin matches the domain of the STUN or
            TURN server in the STUN or TURN URI.  Since web and STUN and
            TURN run on different ports, and often will resolve to
            different IP addresses, a full host comparison is not
            possible.  This proposal is not perfect: it does not provide
            perfect privacy for subdomains (e.g. sub1.example.com
            <https://urldefense.proofpoint.com/v2/url?u=http-3A__sub1.example.com&d=BQMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bwZ-nnRGWmcGKRIuadq6-NSnsgwbBVUJa4mZfmEIBXg&m=YAVYqLAvlnjV5WFeb0DMhGTziYu4jLvpB3UTCbrR8T4&s=rmZxvMmZrZEWtX42fGrg7dcvFr_RUv9ngo2yod2ZHPo&e=>
            and sub2.example.com
            <https://urldefense.proofpoint.com/v2/url?u=http-3A__sub2.example.com&d=BQMFaQ&c=96ZbZZcaMF4w0F4jpN6LZg&r=bwZ-nnRGWmcGKRIuadq6-NSnsgwbBVUJa4mZfmEIBXg&m=YAVYqLAvlnjV5WFeb0DMhGTziYu4jLvpB3UTCbrR8T4&s=AyGtdO3Zale2SSP5BSnM64KJGpiFT9ICrzuSzeBVj7k&e=>
            will match with this rule, even if they are separate
            entities.  Of course, subdomain users could always register
            a new domain and point DNS records to their sub hoster.)

            In comparing this solution against the use cases above:

            1. Allows logging of your own users on your own TURN server
            (or one that you setup DNS SRV records to point towards). 
            Other users of your STUN or TURN server will not be
            identified by an Origin, but you will at least know if
            others are using your server.

            2. Works for REALM selection as long as you use your own
            TURN server (or one that you setup DNS SRV records to point
            towards).

            3. Again, works for service determination as long as you use
            your own TURN server (or one that you setup DNS SRV records
            to point towards). Having service-specific TURN credentials
            is another solution that doesn't rely on ORIGIN.

            4. & 5. Does not seem provide a good solution for these use
            cases.

            Does this analysis make sense?

            Feedback most welcome so we can move forward with this draft.

            - Alan -




-- 
Brandon Williams; Chief Architect
Cloud Networking; Akamai Technologies Inc.