Re: [OAUTH-WG] rfc6749 question about the optional use of the client_id in the request body

[Brian Campbell <[e-mail]>]

Sending the client_id and client_secret in two places is using more than
one authentication method, which isn't allowed. I don't think anyone is
suggesting changing that.

I'm suggesting removing (in errata) the text in the client_secret
definition that says, "The client MAY omit the [client_secret] parameter if
the client secret is an empty string" because it's sometimes led to the
interpretation that the client_id parameter by itself in the body without a
client_secret parameter constitutes a form of client authentication.


On Mon, Jan 29, 2018 at 2:39 PM, Mike Jones <[e-mail]>
wrote:

> I an strongly against sending the client_id and client_secret in two
> places (both in the Authorization: Basic header and in the body).  That’s a
> standard no-no in protocol design because it creates new error cases and
> attacks that otherwise couldn’t exist.  (What do you do if the two values
> don’t match?)
>
>
>
> RFC 6749 suggests that they should be absent from the body if present in
> the header.  (Yes, it’s badly written.)  We shouldn’t screw that up.
>
>
>
>                                                        -- Mike
>
>
>
> *From:* OAuth [mailto:[e-mail]] *On Behalf Of *Brian
> Campbell
> *Sent:* Monday, January 29, 2018 11:58 AM
> *To:* Tom Van Oppens <[e-mail]>
> *Cc:* oauth <[e-mail]>
>
> *Subject:* Re: [OAUTH-WG] rfc6749 question about the optional use of the
> client_id in the request body
>
>
>
> The development of the OAuth 2.0 spec was a rather tumultuous time. That's
> probably true for most standards but I think most would agree that it's
> particularly true for OAuth 2.0. So trying to understand why someone took
> the effort to describe the situation can be a difficult task. I looked back
> in the archives to try and understand the origins of the "client MAY omit
> the [client_secret] parameter if the client secret is an empty string"
> text. It looks as though a few of us (myself included) were advocating to
> have the client_id parameter allowed/defined at the token endpoint in
> general to enable public clients to identify themselves. There was some
> push back from the editor at the time that that didn't fit the model of the
> spec and that instead those clients should be issued an empty secret and
> that text about omitting the client secret when it is an empty string was
> added to draft -21 as a compromise of sorts. It seems kind of silly looking
> back at it and even then the conversation was confusing. But I don't think
> that the intent of the text was ever to have the client_id parameter itself
> be considered a form of authentication that would trigger an error response
> when used in conjunction with another client authentication mechanism.
>
> I don't know that particularly broad changes can be made in errata. So I'd
> propose that the text around client secret in Section 2.3.1 should simply
> say this:
>
>
>
>    client_secret
>
>          REQUIRED.  The client secret.
>
>
> That should take away the potential for interpreting the presence of the
> client_id parameter in the request body as client_secret_post
> authentication when there is no corresponding client_secret parameter. And
> more explicitly allow for other client authentication methods to
> use client_id as needed (as has already happened). That does leave some
> ambiguity with a client_id and http basic but doesn't consider it multiple
> client authentication mechanisms so at least better allows for it. And
> considering Postel's law here along with the reality that some/many clients
> will always send the client_id strongly suggests that such a request not be
> rejected (either ignoring the client_id in that case or checking that it is
> the same as the HTTP basic username).
>
> The example in question in the OIDC spec is using JWT client
> authentication from RFC 7523 that inherits some of its base processing
> rules from RFC 7521, which has the following about client_id. It might be
> difficult to find but I think that much is well defined at least.
>
>    client_id
>
>       OPTIONAL.  The client identifier as described in Section 2.2 <https://tools.ietf.org/html/rfc7521#section-2.2> of
>
>       OAuth 2.0 [RFC6749 <https://tools.ietf.org/html/rfc6749>].  The "client_id" is unnecessary for client
>
>       assertion authentication because the client is identified by the
>
>       subject of the assertion.  If present, the value of the
>
>       "client_id" parameter MUST identify the same client as is
>
>       identified by the client assertion.
>
>
>
>
>
>
>
>
>
>
> On Fri, Jan 26, 2018 at 5:20 AM, Tom Van Oppens <[e-mail]>
> wrote:
>
> @Brian +1
>  I agree that the section is confusing and that errata should be published
> about it, but before we go there it might be interesting why someone took
> the effort to describe the situation with an empty client secret, because
> including these suggestions will break the ability for an sever to dectect
> a double authentication when the client secret is an empty string
>
> - As for the client secret not being an empty, it might be that it's
> updateable by the client.Maybe specifying that a client secret can't be an
> empty string might be the most elegant solution.
> - Secondly I couldn't find the the "If a client_id parameter is present
> in conjunction with some client authentication mechanism, then both must
> refer to the same client. " section nor can i find anywhere in the spec
> what the
>
> I do agree that many to be specs and implementations use the client_id in
> the body, and there are valid arguments to be made for that. But without
> errata in the OAuth2 spec they are violating the OAuth2 spec, And seeing
> the nature of it i think adding errata to the OAuth2 spec is the way to go
>
> Do you have another suggestion to interpret the problematic section ?
>
> @Nat
> Nowhere in the spec i can find that they must match or even that the AS is
> supposed to do anything with it
> When you read the specs at this point the problem is that if a client_id
> is in the body it is the same as a client_id and a secret (but a blank
> secret) and that is a double authentication when the Auth header is present
>
> @all
>
> Shoudln't we define or maybe in the OIDC spec add some information so that
> the AS needs to do something with that clien_id in the body, saying it must
> match the client_id coming in somewhere else ?
> Or at least have the AS do something with it .
>
>
> From:        Nat Sakimura <[e-mail]>
> To:        Brian Campbell <[e-mail]>
> Cc:        Tom Van Oppens <[e-mail]>, oauth <
> [e-mail]>
> Date:        26/01/2018 01:16
> Subject:        Re: [OAUTH-WG] rfc6749 question about the optional use of
> the client_id in the request body
> ------------------------------
>
>
>
>
> +1 to Brian.
>
> I would like to point out that listing the participant in the protocol
> message and the authentication of the message sender is an entirely
> different thing. I see no problems in duplicating client_id in body and
> header. Of course, they have to match and must fail the authentication if
> they do not, but this should not be a problem. In fact, it may even be
> desirable for the message body to have self-contained references to the
> participants in the authentication protocol as shown in [1]. In such a
> case, it will necessarily duplicate in case of the basic authentication.
>
> [1] Basin, D., Cremers, C., Meier, S.: Provably Repairing the ISO/IEC 9798
> Standard for Entity Authentication. Journal of Computer Security - Security
> and Trust Principles archive Volume 21 Issue 6, 817-846 (2013)
>
> Best,
>
> ---
> Nat Sakimura
>
> On Thu, Jan 25, 2018 at 11:28 PM Brian Campbell <
> [e-mail]> wrote:
> Hi Tom,
>
> Indeed RFC 6749 is not well written with respect to this situation and
> unfortunately leaves some room for varied interpretations. However, in my
> own not entirely uninformed view having worked on this stuff for awhile
> now, it is erroneous to interpret the presence of the client_id parameter
> in the request body as client_secret_post authentication when there is no
> corresponding client_secret parameter. As you alluded to, there are other
> types of client authentication that explicitly allow (JWT
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_rfc7521&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=ltDJsK2vgDCcr3IWY5iRsp7x_QzDCvieNa9IgAZy4O0&e=>,
> SAML
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_rfc7522&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=5t-IZXowcm7MIN20j4QOl2BxJaJxFWz-0XlKJ_X0xms&e=>,
> and their base spec
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_rfc7521-23section-2D4.2&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=YD8pI9CXBa4So5_hCdyJdLWxtYItyJwCo9YZ8eR2DiA&e=>)
> or require (MTLS
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_draft-2Dietf-2Doauth-2Dmtls-2D06&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=2A8Zs7FE2MOm62jSvabFzu3FPNNpRiGa3iAgcIX6YJU&e=>)
> the client_id parameter and the OIDC core spec even has an example of the
> client_id parameter in the body
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__openid.net_specs_openid-2Dconnect-2Dcore-2D1-5F0.html-23ClientAuthentication&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=RdRe04BFRix4FU47Mj3lxX9jOi29ZK2qLjn-6LB0wiQ&e=>
> when doing JWT client auth. If client_id with no client_secret in the
> request body actually implies client_secret_post, then those RFCs (one soon
> to be RFC) and OIDF standards are all contradicting OAuth 2.0 /RFC 6749.
> Those supplementary standards as well as widespread
> implementations/deployments in practice should, I believe, be considered
> more authoritative than one particular implementation's problematic (in
> terms of interoperability) interpretation of a not particularly well
> written area of the OAuth spec.
>
> The problematic text from https://tools.ietf.org/html/
> rfc6749#section-2.3.1
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_rfc6749-23section-2D2.3.1&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=oHR04160M5ZlXvS-AxD8FIxmu7FO9yypX4XaEfM9TaI&e=>
> says that "the client MAY omit the [client_secret] parameter if the client
> secret is an empty string" so it would only really be reasonable for an AS
> to reject a request as having two client authentication methods in the case
> that it issued a client the empty string as a client secret (not a public
> client but a client with an empty string as its actual secret), which
> should never happen in practice, and that client sent both a basic
> authorization header without a password and a client_id without a
> client_secret in the body. That's one way to read it anyway. And regardless
> that text in Sec 2.3.1 is problematic and should probably be updated with
> an errata on RFC 6749 to get rid of the text about empty string password
> and just state that the client_secret parameter is required when doing
> client_secret_post authentication. Unfortunately the errata often get
> overlooked but it'd still be good to have that fixed somewhere and a
> published RFC can't be changed so errata is the only real option to
> document the actual intent of the original specification.
>
> The presence of the client_secret parameter should be the only thing that
> implies client_secret_post authentication.
>
> If a client_id parameter is present in conjunction with some client
> authentication mechanism, then both must refer to the same client.
>
>
>
>
> On Wed, Jan 24, 2018 at 3:19 AM, Tom Van Oppens <[e-mail]>
> wrote:
> Dear Oauth Mailing List
>
> After some discussion i had i wanted to ask you for some guidance.
>
> For the following request
>
> * request_uri*
> https://example.com/token
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__example.com_token&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=EDy3oEPZpxW3JhWJwq89LQ66wvTze6bsNrW7kfbsIDo&m=tFxbEJbIhavKlMInYBs8JIzjD8yckAbYak3svMx0cb8&s=UymuwhkQmfGvQJpdKAk5Q7WIUgfoVeZ5Y7efT0_zf3E&e=>
> * request_method*
> POST
> * request_headers*
> {"Accept":"application/json","Authorization":"Basic
> bWFnaWNpZDpwb3RhdG9zZWNyZXQ=","Content-Type":"application/x-
> www-form-urlencoded","Content-Length":"91"}
> * request_body*
> grant_type=client_credentials&scope=accounts&client_id=magicid
>
> We had some discussions whether or not this request is a valid request, to
> be more exact wether the clientid can be in the body.
> Section 2.3.1 states
> * A client MAY use the "client_id" request parameter to identify itself
> when sending requests to the token endpoint. *
>
> But at the same time in the case of a client password (2.3.1)
> The clientid and secret are carried in the basic auth header as a form of
> authentication as a preferred method ,
> But the standard states that if you choose to use the body as a form of
> authentication that if you can ommit the clientsecret the clientsecret is
> an empty string, therefore passing only the client_id is the same as
> passing the client_id and an empty string clientsecret .
>
> So the current request would be according to the spec interpreted as
> follows
> Authentication 1) basic auth cleintid:secret
> Authentication 2) body auth  clientd and blank secret
>
> You can choose to use the client_id in the body with public clients or in
> the confidential client (the Lloyds situation) if you choose to add the
> clientsecret there as well and are not using the basic auth header (this is
> due to spec section 2.3 which states
> * The client MUST NOT use more than one authentication method in each
> request. *
>
> In short there is no way in the spec that allows for the oauth provider to
> distinguish between your intention of sending in the client_id again for
> identification and a malformed request with double authentication.
>
>
> So my stance is (for now) that you cannot send a clientid when you find
> yourself in the clientid with a corresponding password situation.
> Is that a correct statement ?
> and if it is not how would that work ?
> and if it is, when can you send the clientid in the body but use something
> else for authentication  (something like mtls ?) ?
>
> Kind Regards
> Van Oppens Tom
>
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> Nat Sakimura
>
> Chairman of the Board, OpenID Foundation
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>
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