Re: [OAUTH-WG] Mail regarding draft-ietf-oauth-mtls

[Brian Campbell <[e-mail]>]

Thanks Evan.

This seems like a good start and I'll plan to work to incorporate the
proposal in some/similar form into the next revision of the document.
Comments, clarifications, etc. from the WG are also always welcome too in
the meantime. Or from the AD, who also suggested allowing for the use of
SAN. But this seems to generally fit the bill to allow for SAN-based
subject identification of the client in the certificate.

Having thought a bit more about the structured vs. flat metadata, I think
I've come to a similar conclusion as you have.









On Thu, Nov 15, 2018 at 5:41 PM Evan Gilman <[e-mail]> wrote:

> I have taken a stab at some text that will open the door for SAN-based
> subject identity support. Some minor modifications in section 2.1, and
> additional metadata parameters in section 2.1.2. Please find that text
> below.
>
> > I scanned through the SPIFFE docs but didn’t any mentioning of OAuth
> (just plain X.509). What’s your plan for introducing OAuth and mtls?
>
> That is correct - SPIFFE does not currently involve any OAuth works...
> the use case for this change was brought to my attention a couple of
> weeks ago: use SPIFFE identities in "cloud native" environments to
> authenticate to an OAuth server in order to receive an access token
> for authentication with on-prem infrastructure which is OAuth-enabled.
> Doing so relieves a good deal of pressure around OAuth client (and
> secret) management. That said, I think the proposed change here is
> beneficial on all counts, and not just an accommodation for SPIFFE
> authentication. As I mentioned previously, there are several other
> projects that are relying on SAN rather than DN for subject identity
> and the number is growing.
>
> I tried to think through what the text would look like to support a
> structured value for a parameter named `tls_client_auth_san`, but ran
> into a couple sticking points... the first is that it is certainly
> more complex and would require more text, and feels more error prone
> than simply introducing additional metadata parameters. Second, we
> would need to strictly define supported values for `type`, and it
> wasn't immediately clear if this is something that would need to be
> centrally registered. I am curious to hear thoughts on the structured
> value approach versus that which I took below.
>
> 2.1.  PKI Mutual TLS OAuth Client Authentication Method
>
>    The PKI (public key infrastructure) method of mutual TLS OAuth client
>    authentication uses a subject name (DN or SAN) and validated
>    certificate chain to identify the client.  The TLS handshake is
>    utilized to validate the client's possession of the private key
>    corresponding to the public key in the certificate and to validate
>    the corresponding certificate chain.  The client is successfully
>    authenticated if the subject information in the certificate matches
>    the expected subject configured or registered for that particular
>    client (note that a predictable treatment of DN values, such as the
>    distinguishedNameMatch rule from [RFC4517], is needed in comparing
>    the certificate's subject DN to the client's registered DN).  If and
>    how to check a certificate's revocation status is a deployment
>    decision at the discretion of the authorization server.  The PKI
>    method facilitates the way X.509 certificates are traditionally being
>    used for authentication.  It also allows the client to rotate its
>    X.509 certificates without the need to modify its respective
>    authentication data at the authorization server by obtaining a new
>    certificate with the same subject from a trusted certificate
>    authority (CA).
>
> and
>
> 2.1.2.  Client Registration Metadata
>
>    The following metadata parameters are introduced for the OAuth 2.0
>    Dynamic Client Registration Protocol [RFC7591] in support of the PKI
>    method of binding a certificate to a client:
>
>    tls_client_auth_subject_dn
>       An [RFC4514] string representation of the expected subject
>       distinguished name of the certificate, which the OAuth client will
>       use in mutual TLS authentication.
>
>    tls_client_auth_san_dns
>       A string containing the value of an expected dNSName SAN entry
>       in the certificate, which the OAuth client will use in mutual TLS
>       authentication.
>
>    tls_client_auth_san_uri
>       A string containing the value of an expected
>       uniformResourceIdentifier SAN entry in the certificate, which
>       the OAuth client will use in mutual TLS authentication.
>
>    tls_client_auth_san_ip
>       A string representation of an IP address in either dotted decimal
>       notation (for IPv4) or colon-delimited hexadecimal (for IPv6, as
>       defined in [RFC4291] section 2.2) that is expected to be present
>       as an iPAddress SAN entry in the certificate, which the OAuth
>       client will use in mutual TLS authentication.
>
>    tls_client_auth_san_email
>       A string containing the value of an expected rfc822Name SAN
>       entry in the certificate, which the OAuth client will use in
>       mutual TLS authentication.
>
> On Tue, Nov 13, 2018 at 6:24 AM Torsten Lodderstedt
> <[e-mail]> wrote:
> >
> > Hi Evan,
> >
> > I scanned through the SPIFFE docs but didn’t any mentioning of OAuth
> (just plain X.509). What’s your plan for introducing OAuth and mtls?
> >
> > kind regards,
> > Torsten.
> >
> > > Am 13.11.2018 um 00:59 schrieb Evan Gilman <[e-mail]>:
> > >
> > > Thank you everyone for the feedback.
> > >
> > > I am currently working on the sample text, and should be complete in
> > > the next couple days. Apologies for the delay.
> > > On Wed, Nov 7, 2018 at 12:51 AM Brian Campbell
> > > <[e-mail]> wrote:
> > >>
> > >> Sure, I think they could be treated as different different
> client_auth_methods. But there is a lot more commonality than differences
> to the point where I think it makes sense to keep it all in a single
> document and under a single client auth method with just the variation on
> which name is being used.
> > >>
> > >> On Tue, Nov 6, 2018 at 5:11 PM Justin P Richer <[e-mail]>
> wrote:
> > >>>
> > >>> Would it make sense for these to be a different client_auth_method
> entirely? Much the same way that we have private_key_jwt and
> client_secret_jwt today, both of which use the JWT assertion framework but
> have very different keying and security assumptions. In the same way, here
> you’re still validating the cert but the means by which it’s validated is
> different, so the auth method is arguably not going to benefit from being
> overloaded. Caveat, I’ve not built out a system using SANs in any
> meaningful way.
> > >>>
> > >>> If we were to do that, this draft could go forward as-is (since it’s
> fairly done in my opinion) and a new document could better define the
> semantics for the various SAN types, but while building on the framework
> and concepts listed in here.
> > >>>
> > >>> — Justin
> > >>>
> > >>> On Nov 6, 2018, at 3:52 PM, Evan Gilman <[e-mail]> wrote:
> > >>>
> > >>> Response(s) inline
> > >>>
> > >>> On Mon, Nov 5, 2018 at 11:53 PM Neil Madden <
> [e-mail]> wrote:
> > >>>
> > >>>
> > >>> Is there an intention that any semantics are attached to the SAN
> being a URI or DNS name or IP or ...? Or is it still intended to be an
> opaque identifier?
> > >>>
> > >>>
> > >>> There are some extra things we could do if we attached type-specific
> > >>> semantics to the matching (e.g. DNS wildcarding etc), however I think
> > >>> that continuing to use the values as opaque identifiers would get us
> > >>> most of what we need while keeping things simple.
> > >>>
> > >>> On 6 Nov 2018, at 01:55, Brian Campbell <bcampbell=
> [e-mail]> wrote:
> > >>>
> > >>> Thanks Evan for bringing this to the WG's attention. More or less
> the same question/issue was raised yesterday in the area director's review
> of the document as well. I plan to bring this up as a discussion item in
> the meeting today. But my sense from some early discussions is that there
> is likely to be (rough) consensus to make some change in order to allow a
> SAN to be specified as the certificate subject identifier in the PKI client
> auth mode. We'll need to figure out the specifics of how that works. I
> don't think there are significant drawbacks to extending the number of
> client registration metadata parameters per se. I guess I've just been
> attracted to the idea of overloading the existing value because that felt
> like maybe a less invasive change. But perhaps that's shortsighted. And
> there's nothing inherently wrong with additional client metadata parameters.
> > >>>
> > >>> I don't know if we could get away with a single new parameter that
> could carry the value for any SAN type. Something like, { ...
> "tls_client_auth_san": "spiffe://trust-domain/path" ...}. In practice I
> feel like that'd probably be okay but in theory there's the potential for
> confusion of the value across different types. So probably there's a need
> to indicate the SAN type too. Either with more client metadata parameters
> like tls_client_auth_san_uir, tls_client_auth_san_email,
> tls_client_auth_san_ip, etc. or maybe with a structured value of some sort
> like {... "tls_client_auth_san": {"type":"URI",
> "value":"spiffe://trust-domain/path"} ... }. And then deciding which types
> to support and if/how to allow for the extensible types.
> > >>>
> > >>>
> > >>> I am far from an authority here, but it is my understanding that one
> > >>> of the primary drivers in supporting SAN over Subject is that the
> > >>> values are strongly typed. While some of the advantages gained from
> > >>> this may be less useful in our own context, I feel that it make sense
> > >>> to keep the values separate and not overload a single value. Whether
> > >>> that means dedicated metadata parameters or a structured parameter
> > >>> value, I am not sure what the tradeoffs would be, but both options
> > >>> sound suitable to me.
> > >>>
> > >>> Anyway, those are just some thoughts on it. And it'll be discussed
> more today. Suggested/proposed text is always helpful though (even if it's
> not used directly it can help move the conversation forward and/or help
> editor(s) to have prospective wording).
> > >>>
> > >>>
> > >>> Great. I will work on some sample text since it sounds like that
> would
> > >>> be generally helpful
> > >>>
> > >>> On Tue, Nov 6, 2018 at 5:53 AM Evan Gilman <[e-mail]>
> wrote:
> > >>>
> > >>>
> > >>> Hello everyone..
> > >>>
> > >>> Very excited to see this draft. It helps tremendously in addressing
> > >>> use cases around oauth client management in machine-to-machine
> > >>> scenarios. Particularly, the PKI authentication method.
> > >>>
> > >>> In reviewing the document, I noticed that the only supported method
> > >>> for identifying a client using the PKI authentication method is by
> > >>> referencing its distinguished name. This caught me a bit by surprise
> -
> > >>> many newer projects aimed at automating X.509 issuance in the
> > >>> datacenter utilize SAN extensions rather than distinguished name in
> > >>> order to encode identity. I am further under the impression that the
> > >>> community is, in general, moving away from the subject extension
> > >>> altogether in favor of SAN-based identification.
> > >>>
> > >>> Full disclosure: I am one of the maintainers on a project called
> > >>> SPIFFE, which provides identity specifications for datacenter
> workload
> > >>> applications. For X.509, SPIFFE encodes identity into a URI SAN
> > >>> extension. A number of projects using SPIFFE do not configure the
> > >>> subject with identifying information (SPIRE and Google Istio being
> > >>> just a couple). I am also hearing of other X.509 automation projects
> > >>> which are moving away from subject/distinguished name (even if they
> > >>> are not using SPIFFE).
> > >>>
> > >>> While I think support for distinguished name is absolutely necessary,
> > >>> I worry that supporting it solely will render it incompatible with
> > >>> some of the more modern PKIX systems and not stand the test of time.
> I
> > >>> know that I am a little late to this, and for that I apologize... but
> > >>> I feel this is a significant point.
> > >>>
> > >>> I would like to open a discussion on supporting the most commonly
> used
> > >>> SAN extension types in addition to distinguished name. To accomplish
> > >>> this, amending section 2.1.2 `Client Registration Metadata` with
> > >>> additional parameters seems appropriate. In my experience, the most
> > >>> commonly used SAN extensions are: DNS name, IP address, URI, and
> email
> > >>> address.
> > >>>
> > >>> Are there significant drawbacks to extending the number of client
> > >>> registration metadata parameters? I would very much like to see this
> -
> > >>> without it, many existing projects will be unable to use the spec. I
> > >>> am happy to contribute time and text to this, assuming people feel
> > >>> that this is a beneficial addition. Sorry again for the timing
> > >>>
> > >>> --
> > >>> evan
> > >>>
> > >>> _______________________________________________
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> > >>>
> > >>>
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> > >>> --
> > >>> evan
> > >>>
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> > >
> > > --
> > > evan
> > >
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>
>
> --
> evan
>

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