I'm finally getting around to working on the document updates (there's
quite a few things that came out of AD review too). As far as the issue in
this thread goes though, I'm leaning towards adding "mtls_endpoints" as a
new metadata parameter. Maybe mention that a 307 might happen but it'd be
more of a considerations type text.
On Wed, Jan 16, 2019 at 5:52 AM Brian Campbell <bcampb...@pingidentity.com>
wrote:
> I guess I should have also said or been more straightforward in saying
> that I don't particularly want to try and discuss/define the use of a 307
> in the document.
>
> On Tue, Jan 15, 2019 at 6:59 AM Filip Skokan <panva...@gmail.com> wrote:
>
>> I don't know that the use of 307 would need to be discussed in the
>>> document itself.
>>
>>
>> If the clients are supposed to be ready for this, yeah. For instance, my
>> client software by default doesn't follow redirects, in order for it to be
>> ready for mtls client authentication i'd have to know 307 is a possibility
>> and whitelist 307 as a valid code to be followed.
>>
>> S pozdravem,
>> *Filip Skokan*
>>
>>
>> On Tue, Jan 15, 2019 at 2:54 PM Brian Campbell <
>> bcampb...@pingidentity.com> wrote:
>>
>>> I don't know that the use of 307 would need to be discussed in the
>>> document itself.
>>>
>>> On Tue, Jan 15, 2019 at 2:30 AM Filip Skokan <panva...@gmail.com> wrote:
>>>
>>>> I'm in favour of both 307 and metadata.
>>>>
>>>> - case 307 - I don't recall ever encountering an http client
>>>> software that wouldn't have an option for following redirects, same for
>>>> a
>>>> server side frameworks not having the option to do a 307 response with a
>>>> location header.
>>>> - case 307 - Relying purely on a new metadata doesn't help in the
>>>> scenario David put forth earlier about clients not being aware of using
>>>> mtls, a device policy of sorts.
>>>> - case metadata - no second request if the client knows there's an
>>>> mtls endpoint it should use.
>>>>
>>>> Maybe we should specify both as optional for an AS to deploy and a
>>>> client to be ready for?
>>>>
>>>> S pozdravem,
>>>> *Filip Skokan*
>>>>
>>>>
>>>> On Tue, Jan 15, 2019 at 10:05 AM Dave Tonge <
>>>> dave.to...@momentumft.co.uk> wrote:
>>>>
>>>>> I'm in favour of the `mtls_endpoints` metadata parameter - although it
>>>>> should be optional.
>>>>> While a 307 redirect seems kind of elegant I worry, like you, that
>>>>> not all clients would handle it appropriately.
>>>>> There would probably need to be an error defined for clients who
>>>>> attempt to use `tls_client_auth` at the regular endpoint.
>>>>>
>>>>> Dave
>>>>>
>>>>> On Mon, 14 Jan 2019 at 22:29, Brian Campbell <bcampbell=
>>>>> 40pingidentity....@dmarc.ietf.org> wrote:
>>>>>
>>>>>> Trying to summarize things somewhat here and focus in hopefully
>>>>>> towards some decision. There's basically an idea on the table to add an
>>>>>> AS
>>>>>> metadata parameter to the draft-ietf-oauth-mtls doc that would be a JSON
>>>>>> object which contains endpoints that a client doing MTLS would use rather
>>>>>> than the regular endpoints. A straw-man example might look like this
>>>>>> (with
>>>>>> mtls_endpoints being that new parameter).
>>>>>>
>>>>>> {
>>>>>> "issuer":"https://server.example.com";,
>>>>>> "authorization_endpoint":"https://server.example.com/authz";,
>>>>>> "token_endpoint":"https://server.example.com/token";,
>>>>>> "token_endpoint_auth_methods_supported":[
>>>>>> "client_secret_basic","tls_client_auth", "none"],
>>>>>> "userinfo_endpoint":"https://server..example.com/userinfo
>>>>>> <https://server.example.com/userinfo>",
>>>>>> "revocation_endpoint":"https://server.example.com/revo";,
>>>>>> "jwks_uri":"https://server.example.com/jwks.json";,
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> * "mtls_endpoints":{
>>>>>> "token_endpoint":"https://mtls.example.com/token
>>>>>> <https://mtls.example.com/token>", "userinfo_endpoint":"https://mtls
>>>>>> <https://server.example.com/token>.example.com/userinfo
>>>>>> <http://example.com/userinfo>", "revocation_endpoint":"https://mtls
>>>>>> <https://server.example.com/token>..example.com/revo
>>>>>> <http://example.com/revo>" }*
>>>>>> }
>>>>>>
>>>>>> The idea behind this is that "regular" clients (those not doing MTLS)
>>>>>> will use the regular endpoints. And only the host/port of the endpoints
>>>>>> listed in mtls_endpoints will be set up to request TLS client
>>>>>> certificates
>>>>>> during handshake.. Thus any potential impact of the CertificateRequest
>>>>>> message being sent in the TLS handshake can be avoided for all the other
>>>>>> regular clients that are not going to do MTLS - including and most
>>>>>> importantly in-browser javascript clients where there can be less than
>>>>>> desirable UI presented to the end-user.
>>>>>>
>>>>>> The arguments in favor of that seem to be basically that it allows
>>>>>> for AS deployments to support MTLS while still allowing for a "not
>>>>>> broken"
>>>>>> UX for end-users of clients (in-browser javascript clients) that aren't
>>>>>> doing MTLS. And that it's not much in terms of adding to the spec and
>>>>>> complexity of implementations.
>>>>>>
>>>>>> The arguments against it seem to be 1) the bad UX isn't really that
>>>>>> bad and/or will only happen to a subset of users 2) there are other
>>>>>> things
>>>>>> that can be done, such as 307ing or renegotiation/post-handshake client
>>>>>> auth, to avoid the bad UX.
>>>>>>
>>>>>> Speaking for myself, I'm kinda torn on it.
>>>>>>
>>>>>> I will say that, in addition to the folks that have pointed out that
>>>>>> renegotiation just isn't possible in some cases, my experience trying to
>>>>>> do
>>>>>> something like that in the past was not particularly successful or
>>>>>> encouraging. That could have been my fault, of course, but still seems a
>>>>>> relevant data point. I also have my doubts about the actual difficulty of
>>>>>> getting an AS to issue a 307 like response for requests based on the
>>>>>> calling client and the likelihood that some/all OAuth client software
>>>>>> would
>>>>>> handle it appropriately.
>>>>>>
>>>>>>
>>>>>> On Fri, Jan 11, 2019 at 12:32 PM David Waite <
>>>>>> da...@alkaline-solutions.com> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> > On Jan 11, 2019, at 3:32 AM, Neil Madden <
>>>>>>> neil.mad...@forgerock.com> wrote:
>>>>>>> >
>>>>>>> > On 9 Jan 2019, at 05:54, David Waite <da...@alkaline-solutions.com>
>>>>>>> wrote:
>>>>>>> >>
>>>>>>> >>> On Dec 28, 2018, at 3:55 PM, Brian Campbell <bcampbell=
>>>>>>> 40pingidentity....@dmarc.ietf.org> wrote:
>>>>>>> >>>
>>>>>>> >> <snip>
>>>>>>> >>
>>>>>>> >>> All of that is meant as an explanation of sorts to say that I
>>>>>>> think that things are actually okay enough as is and that I'd like to
>>>>>>> retract the proposal I'd previously made about the MTLS draft
>>>>>>> introducing a
>>>>>>> new AS metadata parameter. It is admittedly interesting (ironic?) that
>>>>>>> Neil
>>>>>>> sent a message in support of the proposal as I was writing this. It did
>>>>>>> give me pause but ultimately didn't change my opinion that it's not
>>>>>>> worth
>>>>>>> it to add this new AS metadata parameter.
>>>>>>> >>
>>>>>>> >> Note that the AS could make a decision based on the token
>>>>>>> endpoint request - such as a policy associated with the “client_id”, or
>>>>>>> via
>>>>>>> a parameter in the ilk of “client_assertion_type” indicating MTLS was
>>>>>>> desired by this public client installation. The AS could then to TLS 1.2
>>>>>>> renegotiation, 1.3 post-handshake client authentication, or even use 307
>>>>>>> temporary redirects to another token endpoint to perform mutual
>>>>>>> authentication.
>>>>>>> >
>>>>>>> > Renegotiation is an intriguing option, but it has some practical
>>>>>>> difficulties. Our AS product runs in a Java servlet container, where it
>>>>>>> is
>>>>>>> pretty much impossible to dynamically trigger renegotiation without
>>>>>>> accessing private internal APIs of the container. I also don’t know how
>>>>>>> you
>>>>>>> could coordinate this in the common scenario where TLS is terminated at
>>>>>>> a
>>>>>>> load balancer/reverse proxy?
>>>>>>> >
>>>>>>> > A 307 redirect could work though as the server will know if the
>>>>>>> client either uses mTLS for client authentication or has indicated that
>>>>>>> it
>>>>>>> wants certificate-bound access tokens, so it can redirect to a
>>>>>>> mTLS-specific endpoint in those cases.
>>>>>>>
>>>>>>> Agreed. There are trade-offs for both. As you say, I don’t know a
>>>>>>> way to have say a custom error code or WWW-Authenticate challenge to
>>>>>>> trigger renegotiation on the reverse proxy - usually this is just a
>>>>>>> static,
>>>>>>> location-based directive.
>>>>>>>
>>>>>>> >
>>>>>>> >> Both the separate metadata url and a “client_assertion_type”-like
>>>>>>> indicator imply that the client has multiple forms of authentication
>>>>>>> and is
>>>>>>> choosing to use MTLS. The URL in particular I’m reluctant to add support
>>>>>>> for, because I see it more likely a client would use MTLS without
>>>>>>> knowing
>>>>>>> it (via a device-level policy being applied to a public web or native
>>>>>>> app)
>>>>>>> than the reverse, where a single client (represented by a single
>>>>>>> client_id)
>>>>>>> is dynamically picking between forms of authentication.
>>>>>>> >
>>>>>>> > That’s an interesting observation. Can you elaborate on the sorts
>>>>>>> of device policy you are talking about? I am aware of e.g. mobile device
>>>>>>> management being used to push client certificates to iOS devices, but I
>>>>>>> think these are only available in Safari.
>>>>>>>
>>>>>>> The primary use is to set policy to rely on device level management
>>>>>>> in controlled environments like enterprises when available. So an AS may
>>>>>>> try to detect a client certificate as an indicator of a managed device,
>>>>>>> use
>>>>>>> that to assume a device with certain device-level authentication, single
>>>>>>> user usage, remote wipe, etc. characteristics, and decide that it can
>>>>>>> reduce user authentication requirements and/or expose additional scopes.
>>>>>>>
>>>>>>> On more thought, this is typically done as part of the user agent
>>>>>>> hitting the authorization endpoint, as a separate native application
>>>>>>> may be
>>>>>>> interacting with the token endpoint, and in some operating systems the
>>>>>>> application’s network connections do not utilize (and may not have
>>>>>>> access
>>>>>>> to) the system certificate store.
>>>>>>>
>>>>>>> In terms of user agents, I believe you can perform similar behavior
>>>>>>> (managed systems using client certificates on user agents
>>>>>>> transparently) on
>>>>>>> macOS, Windows, Chrome, and Android devices, Chrome (outside iOS)
>>>>>>> typically
>>>>>>> inherits device level policy. Firefox on desktop I assume you can do
>>>>>>> that
>>>>>>> in limited fashion as well.
>>>>>>>
>>>>>>> -DW
>>>>>>
>>>>>>
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