[OAUTH-WG] MTLS token endoint & discovery

[Dominick Baier <[e-mail]>]

We are currently implementing MTLS in IdentityServer.

Our approach will be that we’ll offer a separate token endpoint that
supports client certs. Are you planning on adding an official endpoint name
for discovery? Right now we are using “mtls_token_endpoint”.

Thanks
———
Dominick

On 7. February 2019 at 22:36:55, Brian Campbell (
bcampbell=[e-mail]) wrote:

Ah yes, that makes sense. Thanks for clarifying. And it is indeed a good
reminder that even a seemingly innocuous change that should be backwards
compatible can break things unexpectedly..





On Thu, Feb 7, 2019 at 8:57 AM Richard Backman, Annabelle <
[e-mail]> wrote:

> The case I’m referencing didn’t specifically involve AS metadata. We had
> clients in the wild that assumed that all the properties in the JSON object
> returned from our userinfo endpoint were scalar strings. This broke when we
> introduced a new property whose value was a JSON object. It was a good
> reminder that even a seemingly innocuous change that should be backwards
> compatible can force more work on clients than we expect.
>
>
>
> --
>
> Annabelle Richard Backman
>
> AWS Identity
>
>
>
>
>
> *From:* Brian Campbell <[e-mail]>
> *Date:* Wednesday, February 6, 2019 at 11:30 AM
> *To:* "Richard Backman, Annabelle" <richanna=[e-mail]>
> *Cc:* "Richard Backman, Annabelle" <[e-mail]>, oauth <
> [e-mail]>
> *Subject:* Re: [OAUTH-WG] [UNVERIFIED SENDER] Re: MTLS and in-browser
> clients using the token endpoint
>
>
>
> And I'm honestly really struggling to see what could have gone wrong with
> or how token_endpoint_auth_methods broke something with the user info
> endpoint. If you have the time and/or it'd be informative to this here
> little discussion, please explain that one a bit more.
>
>
>
> On Wed, Feb 6, 2019 at 12:15 PM Brian Campbell <[e-mail]>
> wrote:
>
> "far" should have said "fair" in the previous message
>
>
>
>
>
>
>
>
>
>
>
> On Tue, Feb 5, 2019 at 4:35 PM Brian Campbell <[e-mail]>
> wrote:
>
> It may well be due to my own intellectual shortcomings but these
> issues/questions/confusion-points are not resonating for me as being
> problematic.
>
>
>
> The more general stance of "this isn't needed or worth it in this
> document" (I think that's far?) is being heard though.
>
>
>
>
>
>
>
> On Tue, Feb 5, 2019 at 1:42 PM Richard Backman, Annabelle <richanna=
> [e-mail]> wrote:
>
> (TL;DR: punt AS metadata to a separate draft)
>
> AS points #1-3 are all questions I would have as an implementer:
>
>    1. Section 2 of RFC8414 <https://tools.ietf.org/html/rfc8414#section-2>
>    says token_endpoint “is REQUIRED unless only the implicit grant type is
>    supported.” So what does the mTLS-only AS put here?
>    2. The claims for these other endpoints are OPTIONAL, potentially
>    leading to inconsistency depending on how #1 gets decided.
>    3. The example usage of the token_endpoint_auth_methods property given
>    earlier is incompatible with RFC8414, since some of its contents are only
>    valid for the non-mTLS endpoints, and others are only valid for the mTLS
>    endpoints. Hence this question.
>    4. This introduces a new metadata property that could impact how other
>    specs should extend AS metadata. That needs to be addressed.
>
>
>
> I could go on for client points but you already get the point. Though I’ll
> share that #3 is real and once forced me to roll back an update to the
> Login with Amazon userinfo endpoint…good times. 😃
>
>
>
> I don’t necessarily think an AS metadata property is wrong per se, but
> understand that you’re bolting a layer of flexibility onto a standard that
> wasn’t designed for that, and I don’t think the metadata proposal as it’s
> been discussed here sufficiently deals with the fallout from that. In my
> view this is a complex enough issue and it’s for a nuanced enough use case
> (as far as I can tell from discussion? Please correct me if I’m wrong) that
> we should punt it to a separate draft (e.g., “Authorization Server Metadata
> Extensions for mTLS Hybrids”) and get mTLS out the door.
>
>
>
> --
>
> Annabelle Richard Backman
>
> AWS Identity
>
>
>
>
>
> *From:* OAuth <[e-mail]> on behalf of Brian Campbell
> <bcampbell=[e-mail]>
> *Date:* Monday, February 4, 2019 at 5:28 AM
> *To:* "Richard Backman, Annabelle" <richanna=[e-mail]>
> *Cc:* oauth <[e-mail]>
> *Subject:* Re: [OAUTH-WG] [UNVERIFIED SENDER] Re: MTLS and in-browser
> clients using the token endpoint
>
>
>
> Those points of confusion strike me as somewhat hypothetical or
> hyperbolic. But your general point is taken and your position of being anti
> additional metadata on this issue is noted.
>
>
>
> All of which leaves me a bit uncertain about how to proceed. There seem to
> be a range of opinions on this point and gauging consensus is proving
> elusive for me. That's confounded by my own opinion on it being somewhat
> fluid.
>
>
>
> And I'd really like to post an update to this draft about a month or two
> ago.
>
>
>
>
>
>
>
>
>
>
>
>
>
> On Fri, Feb 1, 2019 at 5:03 PM Richard Backman, Annabelle <richanna=
> [e-mail]> wrote:
>
> Confusion from the AS’s perspective:
>
>    1. If I only support mTLS, do I need to include both
>    token_endpoint_uri and mtls_endpoints? Should I omit token_endpoint_uri? Or
>    set it to the empty string?
>    2. What if I only support mTLS for the token endpoint, but not
>    revocation or user info?
>    3. How do I specify authentication methods for the mTLS token
>    endpoint? Does token_endpoint_auth_methods apply to both the mTLS and
>    non-mTLS endpoints?
>    4. I’m using the OAuth 2.0 Device Flow. Do I include a mTLS-enabled
>    device_authorization_endpoint under mtls_endpoints?
>
>
>
> Confusion from the client’s perspective:
>
>    1. As far as I know, I’m a public client, and don’t know anything
>    about mTLS, but the IT admins installed client certs in their users’
>    browsers and the AS expects to use that to authenticate me.
>    2. My AS metadata parser crashed because the mTLS-only AS omitted
>    token_endpoint_uri.
>    3. My AS metadata parser crashed because it didn’t expect to encounter
>    a JSON object as a parameter value.
>    4. The mTLS-only AS didn’t provide a value for mtls_endpoints, what do
>    I do?
>    5. I don’t know what that “m” means, but they told me to use HTTPS, so
>    I should use the one with “tls” in its name, right?
>
>
>
> Yes, you can write normative text that answers most of these. But you’ll
> have to clearly cover a lot of similar-but-slightly-different scenarios and
> be very explicit. And implementers will still get it wrong. The metadata
> change introduces opportunities for confusion and failure that do not exist
> now, and forces them on everyone who supports mTLS. In contrast, the 307
> redirect is only required when an AS wants to support both, and is
> unambiguous in its behavior and meaning.
>
>
>
> --
>
> Annabelle Richard Backman
>
> AWS Identity
>
>
>
>
>
> *From:* Brian Campbell <bcampbell=[e-mail]>
> *Date:* Friday, February 1, 2019 at 3:17 PM
> *To:* "Richard Backman, Annabelle" <[e-mail]>
> *Cc:* George Fletcher <[e-mail]>, oauth <[e-mail]>
> *Subject:* [UNVERIFIED SENDER] Re: [OAUTH-WG] MTLS and in-browser clients
> using the token endpoint
>
>
>
> It doesn't seem like that confusing or large of a change to me - if the
> client is doing MTLS and the given endpoint is present in `mtls_endpoints`,
> then it uses that one.  Otherwise it uses the regular endpoint. It gives an
> AS a lot of flexibility in deployment options. I personally think getting a
> 307 approach deployed and working would be more complicated and error
> prone.
>
>
>
> It is a minority use case at the moment but there are forces in play, like
> the push for increased security in general and to have javascript clients
> use the code flow, that suggest it won't be terribly unusual to see an AS
> that wants to support MTLS clients and javascript/spa clients at the same
> time.
>
>
>
> I've personally wavered back and forth in this thread on whether or not to
> add the new metadata (or something like it). With my reasoning each way
> kinda explained somewhere back in the 40 or so messages that make up this
> thread.  But it seems like the rough consensus of the group here is in
> favor of it.
>
>
>
>
>
>
>
>
>
> On Fri, Feb 1, 2019 at 3:18 PM Richard Backman, Annabelle <richanna=
> [e-mail]> wrote:
>
> This strikes me as a very prominent and confusing change to support what
> seems to be a minority use case. I’m getting a headache just thinking about
> the text needed to clarify when the AS should provide `mtls_endpoints` and
> when the client should use that versus using `token_endpoint.` Why is the
> 307 status code insufficient to cover the case where a single AS supports
> both mTLS and non-mTLS?
>
>
>
> --
>
> Annabelle Richard Backman
>
> AWS Identity
>
>
>
>
>
> *From:* OAuth <[e-mail]> on behalf of Brian Campbell
> <bcampbell=[e-mail]>
> *Date:* Friday, February 1, 2019 at 1:31 PM
> *To:* George Fletcher <gffletch=[e-mail]
> <40aol.com@dmarc....ietf.org>>
> *Cc:* oauth <[e-mail]>
> *Subject:* Re: [OAUTH-WG] MTLS and in-browser clients using the token
> endpoint
>
>
>
> Yes, that would work.
>
>
>
> On Fri, Feb 1, 2019 at 2:28 PM George Fletcher <gffletch=
> [e-mail]> wrote:
>
> What if the AS wants to ONLY support MTLS connections. Does it not specify
> the optional "mtls_endpoints" and just use the normal metadata values?
>
> On 1/15/19 8:48 AM, Brian Campbell wrote:
>
> It would definitely be optional, apologies if that wasn't made clear. It'd
> be something to the effect of optional for the AS to include and clients
> doing MTLS would use it when present in AS metadata.
>
>
>
> On Tue, Jan 15, 2019 at 2:04 AM Dave Tonge <[e-mail]>
> wrote:
>
> I'm in favour of the `mtls_endpoints` metadata parameter - although it
> should be optional.
>
>
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