Re: [OAUTH-WG] Client Instances of An Application - Was: Re: Last call review of draft-ietf-oauth-dyn-reg-10

Justin Richer <> Tue, 21 May 2013 13:46 UTC

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From: Justin Richer <>
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Subject: Re: [OAUTH-WG] Client Instances of An Application - Was: Re: Last call review of draft-ietf-oauth-dyn-reg-10
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On 05/21/2013 02:01 AM, Phil Hunt wrote:
> Phil
> On 2013-05-20, at 8:35, Justin Richer < 
> <>> wrote:
>> On 05/17/2013 05:27 PM, Phil Hunt wrote:
>>> Mike,
>>> Rather then embed comments in an extended thread, I'd like to open 
>>> up a specific discussion on the objective of dyn reg.
>>> I see limited to no value in having clients completely anonymously 
>>> registering and receiving tokens without any ability to correlate 
>>> applications between applications.
>> I think that herein lies a very big disconnect in assumptions. I see 
>> a huge benefit in anonymously registered clients getting tokens 
>> because there is an end-user in the loop during the authorization 
>> phase (long after registration has happened). The arity of 
>> registrations to authorizations approaches 1:1 in these cases, and 
>> I'm just fine with that.
> <Ph>Then what you describe is NOT anonymous but rather a profile not 
> covered by the spec as there is no discussion of user authenticated 
> registration. Implicitly or explicitly.

[JR] I think you misunderstand what I said, let me try to be more 
explicit: the user is not authenticating the registration. The user is 
not involved in the registration. The user might not even know that a 
registration happened. The registration is (normally) completely 
anonymous and open, the client just shows up and says "Hi, I'm a client!".

The "authorization" that I mentioned happens later and is a normal OAuth 
authorization, which has a user involved like usual. The authorization 
step in OAuth depends on *some* kind of registration happening 
beforehand, dynamic or otherwise. This is all perfectly within the model 
of OAuth.

>> From the RFC6749 perspective, a "client" is not a particular piece of 
>> code, it is a particular copy of a piece of code with a particular 
>> client_id from the vantage point of a particular authorization server.
> <ph> actually, i disagree. This spec fundamentally breaks the old 
> definition and behavior from 6749. In the old way every instance of 
> software shared a client_id. In this draft, u throw that away without 
> preserving the information. This is BAD!
[JR] No, we're not throwing that away at all. The concept is the same, 
but when you add new functionality, the mechanics change a bit. A 
"client_id" was always pairwise between a client and an AS. If a client 
had to talk to two AS's before, it would have two client_ids. That's 
still the case. If there were multiple copies of a confidential client, 
you need to get a client_id and client_secret to each copy. That's still 
the case. What's different is that we've made it *easier* for a 
particular piece of code to get different client_ids when it's talking 
to the same or a different auth server, at runtime. When you have to 
manually register every client, you're going to just do it once. If you 
can do it dynamically, you have more options.

Note that you can *still* have a public client with a known client_id if 
you want to. You don't even need to use dynamic registration for that. 
Heck, you don't need to use dynamic registration for any kind of client 
if you don't want to, since most services will probably still offer 
manual registration through some portal kind of page.

>> A "client" is, conceptually, a pairwise association between two 
>> running codebases. When you have a particular piece of code talking 
>> only to one auth server and being manually configured at said auth 
>> server with its client_id, this is fairly clear and straightforward 
>> and the arity is simple. Things get a bit muddy when you introduce 
>> dynamic registration, which is why I think that we need to have 
>> introductory text about this. Specifically:
>>  - a particular piece of code can be run on multiple devices and talk 
>> to the same auth server, each copy of that code getting its own 
>> client_id.
>>  - a particular copy of a particular piece of code can now be 
>> expected to talk to multiple auth servers, each auth server giving 
>> the piece of code its own client_id.
>> Both of these are cases of what defines an "instance" in most 
>> people's heads, even though it's the same software, even sometimes 
>> the same running copy of the same software. But as far as RFC6749's 
>> definition of "client" is concerned, these are all completely 
>> separate "client"s with no way to tie them together out of the box. 
>> And that's fine.
>>> Associating client_id's with known client applications to allow 
>>> admins to know who is running what version of clients seems to be 
>>> the most fundamental part of the reason for dynamic reg. How can you 
>>> revoke access to particular client app types?  As Justin already 
>>> talked about in his Blue Button+ scenario, there are often life and 
>>> death situations where particular sets of clients need to be revoked.
>> While it's very useful, I wouldn't (and haven't) classified it quite 
>> like that. Nor would I say that the BB+ profile is a complete 
>> solution -- our Registry component does not actually push revocation 
>> notifications down to Providers (yet), so it's more like invalidating 
>> a root certificate and waiting for caches to time out for things to 
>> cascade. We've been talking about adding some form of callback to 
>> providers, but we don't want to boil that particular ocean right now. 
>> However, the BB+ profile makes use of a well-specified discovery and 
>> Registry set up, as well as data conveyed in structured, signed 
>> tokens (JWTs) at different points in the process.
>>> Or put another way. I believe this will be a critical operational 
>>> requirement going forwards. If the spec is published as is, it will 
>>> be quickly invalidated by one that does at least partially address 
>>> the problem.
>> That's not true at all. BB+ addresses this scenario and still uses 
>> the Dynamic Registration spec as-is. I would encourage folks to read 
>> what we're doing, a work-in-progress found here:
> <ph> but you are breaking other things and overloading client cred etc 
> to pass in signed data. I don't want a hack for a solution. I want 
> interop.
[JR] I'm curious, what exactly are we breaking? If anything in BB+ 
breaks compatibility with OAuth Dyn Reg, that's a mistake in BB+ that we 
need to fix there. It is our intent to be fully compatible with OAuth 
Dyn Reg, and we are even explicitly calling for open registration as 
mandatory to implement for authorization servers within BB+, even though 
we have additional mechanisms as well for what we're calling "trusted 
registrations". For those trusted registrations, we're not using the 
client *credentials* to pass in signed data, we're using the initial 
*registration authentication* mechanism (which is to say, an OAuth 
token) for its intended purpose: authorizing the holder of this token 
access to the registration endpoint. In BB+, we're profiling exactly 
what that means. To wit, we define the content of the token (which is 
fully compatible with DynReg which doesn't care what's in the token) and 
how the AS can verify it (which DynReg doesn't care how it happens) and 
we've added some additional rules and policies that allow us to tie 
together instances of the client across the distributed network.

So why doesn't DynReg adopt this mechanism? Two reasons: it adds a huge 
amount of very specific machinery (signed tokens with known formats and 
fields, a Registry with manual pre-registration, a three-tiered 
discovery service with information about clients and service providers 
rooted at the Registry, trust frameworks and network enforcement 
policies that all players have to agree to before playing, etc.), and 
it's not really doing just registration anymore. In BB+, we needed the 
Registry and Discovery services to do other functions as well apart from 
just registration, and so it makes sense to re-use them.

If there were a simple solution that didn't leave security holes the 
size of a small army, I'd be glad to bring it to the table. But I am 
convinced that a good solution for managing client instances across a 
network requires a lot more thought and consideration, and I believe 
that having a fully specified discovery service will help this case, 
like it has helped in BB+. But I think that it's a complex enough 
problem that it needs its own set of considerations. With DynReg, we 
need to leave things open for that work in the future, and I believe we 
have, but we shouldn't kill the simple, general case for want of a 
special case.

>> Just because you make something better doesn't mean you throw 
>> necessarily away everything you've done to date.
>>> We're ahead of schedule, lets talk through the requirement.
>> I believe that the requirement of tying instances together is 
>> explicitly out of scope for the dynamic registration protocol. I 
>> intended to have text to that effect in the section I'm adding about 
>> the client lifecycle.
> <ph> where is this stated in charter?
[JR] The charter for the working states what's in scope, not what's out 
of scope, correct? It has been my understanding of IETF process that 
additional functionality needs to be considered separately. All the 
charter says about registration is this:

    And dynamic client registration will make
    it easier to broadly deploy OAuth clients (performing services to


    Sep 2013 Submit 'OAuth Dynamic Client Registration Protocol' to the
    IESG for consideration as a Proposed Standard

There's nothing in there at all about tying together client instances. I 
have not seen anything to convince me that management of client 
instances across a deployed network of auth servers is a necessary part 
of basic client registration. It sounds very likely to me that it *is* 
required for your use case, but that doesn't make it required for 
everybody's use case.

There are other important pieces of functionality that the WG isn't 
picking up right now (such as token chaining and token introspection) 
that are absolutely necessary for my own use cases, but I think it makes 
sense for those to be separate modules.

>>> As I mentioned in my comments to the other thread. Let's say we 
>>> agree not do this now. Well, then the new draft that does solve it 
>>> would likely be 95% overlap.  Thus I see this issue as within 
>>> charter and should be solved now rather then waiting for a V2 dyn 
>>> reg in the next charter.
>> Why wouldn't the new draft just be the extra 5%? I personally think 
>> that it's a lot more than 5% once you have in all the assurance and 
>> safety mechanisms in place to avoid self-asserted values causing race 
>> conditions, and what not.
> <ph> Two drafts to do registration is not the way to go. It implies 
> complexity where there should be none. There is no technical reason 
> for two drafts.
[JR] There is a need when there's a special case that requires a large 
amount of overhead to be done correctly, to allow the general case to 
move forward and be used on its own (as it is being used today).

>>  -- Justin
>>> Phil
>>> @independentid
>>> <>
>>> <>
>>> On 2013-05-17, at 1:08 PM, Mike Jones wrote:
>>>> Thanks for the detailed feedback, Phil.  Sorry for the delayed 
>>>> response – I was pretty fully engaged at the European Identity 
>>>> Conference (whereOAuth 2.0 won the award for best new standard 
>>>> <>J). My feedback on the points 
>>>> raised is inline in green…
>>>> (Perhaps if any of you reply to this thread, you could also choose 
>>>> a distinctcolorfor your inline replies, so that it will be easily 
>>>> evident who said what.  As it is, just the back-and-forth between 
>>>> Phil and Justin is already very difficult to follow. Thanks.)
>>>> *From:* 
>>>> <>[]*On 
>>>> Behalf Of*Phil Hunt
>>>> *Sent:*Thursday, May 16, 2013 12:54 PM
>>>> *To:*Richer, Justin P.
>>>> *Cc:* <>WG
>>>> *Subject:*Re: [OAUTH-WG] Last call review of 
>>>> draft-ietf-oauth-dyn-reg-10
>>>> Justin,
>>>> Thanks for the discussion. More comments below...
>>>> BTW. I'm happy to contribute text. Just want to get to some rough 
>>>> agreement first.  For example, I think we need to have a away to 
>>>> recognize two pieces of software as being the same (even if 
>>>> self-asserted).  Once defined, I can put together some intro text, etc.
>>>> Phil
>>>> @independentid
>>>> <>
>>>> <>
>>>> On 2013-05-16, at 5:16 AM, Richer, Justin P. wrote:
>>>> On May 15, 2013, at 10:30 PM, Phil Hunt < 
>>>> <>>
>>>>  wrote:
>>>> On 2013-05-15, at 5:53 PM, Richer, Justin P. wrote:
>>>> Phil, many thanks for the extremely thorough review! It is very 
>>>> useful indeed.
>>>> My comments and responses to each point are inline.
>>>> On May 15, 2013, at 4:30 PM, Phil Hunt < 
>>>> <>> wrote:
>>>> It seems unfortunate that I have not gotten a chance to get into 
>>>> this level of detail much earlier. But then, I guess that's what LC 
>>>> review is for! My apologies for not getting many of these concerns 
>>>> to the WG much earlier.
>>>> */Overall /*
>>>> -----------
>>>> I think dynamic registration is a critical part of the OAuth 
>>>> framework now that we are starting to consider how individual 
>>>> client applications should operate when there is one or more 
>>>> deployments of a particular resource API. We've moved from the 
>>>> simple use case of a single API provider like Facebook or Flickr 
>>>> and moved on to standards based, open source based, and commercial 
>>>> based deployments where there are multiple service endpoints and 
>>>> many clients to manage.
>>>> The dynamic registration spec is actually dealing with a couple of 
>>>> issues that I would like to see made more clear in early part of 
>>>> the spec:
>>>> 1.  How is a new client application recognized for the first time 
>>>> when deployed against a particular SP endpoint?  Should clients 
>>>> actually assert an application_id UUID that never changes and 
>>>> possibly a version id that does change with versions?
>>>> In the general case, why is any recognition required? If you're 
>>>> doing things as part of a larger protocol ecosystem, like Blue 
>>>> Button+ or a particular OpenID Connect provider, then you can 
>>>> define semantics for tying together classes of clients (see below 
>>>> for more discussion on this very point). But in general, a client 
>>>> is just going to show up as a new instance to the AS and get issued 
>>>> a new, unique client_id, and that's that.
>>>> I think we have to define more clearly what an "instance" is. For 
>>>> me, there are applications and there are instances of that 
>>>> application.  It is useful to understand that a client application 
>>>> represents a set of code that should behave in a consistent way. 
>>>>  It seems to me the first time a new application shows up is very 
>>>> different from the subsequent instances that register. For example, 
>>>> after the first registration, subsequent instances don't need 
>>>> special review or approval to the same degree.
>>>> But without other mechanisms to tie things together, there's no way 
>>>> for an authorization server to know if any client instance is tied 
>>>> to any other client instance. Therefore, from the perspective of an 
>>>> AS, the first instance of an application (i.e., particular 
>>>> configuration of a set of code) to register is no different to 
>>>> subsequent instances of that same application. How were you 
>>>> envisioning an AS knowing the difference between the first and 
>>>> subsequent instances of an application, specifically? If there's an 
>>>> "application_id" like you mention above, I think it raises more 
>>>> questions than it resolves: Who issues the application_id, some 
>>>> server or the application itself? Is it validated at all? Should it 
>>>> be considered secret? What happens when someone simply steals an 
>>>> application_id? Does an AS have to do anything to check with any 
>>>> other AS to see if the application_id has already been used elsewhere?
>>>> I do agree that a discussion of "instance vs. application" would be 
>>>> helpful in clearing this up, I'll make a note to add text to that 
>>>> effect. (We had to do something similar for BB+)
>>>> I think it is simple enough to at least add a self generated UUID 
>>>> for the application ID.  Though I would allow for cases where the 
>>>> application ID is assigned when the client developer and the APIs 
>>>> owner do a formal assignment of application IDs.
>>>> In a sense this is just a lower tech way of doing it than what you 
>>>> described as the initial client credential in Blue Button+ where 
>>>> you encoded extra claims into the initial app credential.
>>>> What the UUID does is link multiple instances of a client app 
>>>> together as the same "thing" that should have similar 
>>>> heuristics/behaviours.  This is very useful if you want to be able 
>>>> to revoke access to a set of clients identified by application id 
>>>> (or a version of that app).
>>>> While I’m sympathetic to the OAuth working group eventually doing 
>>>> work on differentiating between instances of an OAuth client, I’ll 
>>>> note that in RFC 6749 or RFC 6750 there is no such thing as a 
>>>> client instance. There are only clients, which are identified by 
>>>> client_id values.  If we want to do work on client instances, we 
>>>> should recharter to add this new work as a working group 
>>>> deliverable.  We should not try to shoehorn bits and pieces of it 
>>>> into the Dynamic Registration spec, any more than we should have 
>>>> tried to shoehorn it into RFC 6749 or RFC 6750.  Oauth-dyn-reg is 
>>>> there to register clients as defined in RFC 6749.  It’s not the 
>>>> right place to extend what an OAuth client is in new ways.
>>>>         2.  How are client credentials managed. Are we assuming
>>>>         client credentials have a limited lifetime or rotation policy?
>>>>         The intent was that client_secret could be rotated, as
>>>>         indicated by the expires_at member of the response. If a
>>>>         client's secret expires, it calls the read operation on the
>>>>         Client Configuration Endpoint (§4.2) to get its new
>>>>         client_secret. If this is unclear in the current text
>>>>         (which I suspect it may be after multiple refactorings),
>>>>         then I welcome suggestions and specific text as to how to
>>>>         make that clear.
>>>>     Something like this should be in the draft.
>>>>     Should this be up in the introductory text, somewhere else, or
>>>>     have its own section?
>>>> I'm starting to think credential management is a key part of the 
>>>> draft. It may be worth introducing a specific section outling the 
>>>> registration life-cycle, registration access token usage, and 
>>>> client token usage and bootstrapping.
>>>> I think that adding a discussion on this would be fine, as it could 
>>>> help developers understand the workflow of registering, using, and 
>>>> updating registered clients.
>>>>     How does a client authenticate the first time and subsequent
>>>>     times to the registration service?
>>>>     This is a separate question all together, as it does not
>>>>     involve the client_secret or client_id at all. Rather, the
>>>>     first time the client shows up to the registration service, it
>>>>     may either:
>>>>       - Not authenticate at all (this is the true public, open
>>>>     registration, and it is recommended that servers do this)
>>>>      - Authenticate using an OAuth 2.0 token (which ATM means a
>>>>     bearer token). How the client gets that bearer token and what
>>>>     the bearer token means to the AS beyond "this client is
>>>>     authorized to register" is out of scope for the spec, by design.
>>>>     Subsequent times that the same registered client (by which we
>>>>     mean the same instance of a client with a particular client_id)
>>>>     shows up at the registration endpoint (actually, the Client
>>>>     Configuration Endpoint), it uses its Registration Access Token
>>>>     that it was issued on initial registration. This is an OAuth
>>>>     2.0 Bearer token that is unique to the client instance.
>>>> Something like this should be in the draft.
>>>> OK, the definition of the registration access token can be 
>>>> expanded, but I think that the rest of it is already in there in 
>>>> §3. I'd welcome suggestions on which bits of this could be made 
>>>> clearer.
>>>> See the discussion on what the registration_access_token is in the 
>>>> thread “Client Credential Expiry and new Registration Access Token 
>>>> - draft-ietf-oauth-dyn-reg-10”.  I will work with Justin to apply 
>>>> these clarifications to the specification.  This may go into the 
>>>> proposed credential management overview section discussed above.
>>>>         3.  How is versioning of clients managed? Should each new
>>>>         version of a client require a change in client registration
>>>>         including possibly changing client_id and authentication
>>>>         credential? I don't have a strong feeling, but it is
>>>>         something that implementors should consider.
>>>>     This is up to the AS, really, and I don't think that any global
>>>>     policy would ever fly here. Especially if you consider that the
>>>>     entire notion of "version" is more fluid these days than it
>>>>     ever has been. I wouldn't mind adding a discussion in the
>>>>     security considerations if it merits mentioning though, so that
>>>>     we can help both client developers and server developers
>>>>     institute reasonably good policy.
>>>> I guess the issue is that when a client upgrades it may have access 
>>>> to the old credentials. What is the intent then of registration. 
>>>>  Since you have an update are clients expected to update 
>>>> /re-register or not?  I'm not sure this is a security consideration 
>>>> but more part of the whole change management function dynamic 
>>>> registration supports.
>>>> If your upgraded version of the client still has access to its old 
>>>> credentials, why wouldn't it just use those? I don't see a reason 
>>>> for forcing a re-registration. Nor do I see any way that an AS 
>>>> would even be able to tell that a client had been upgraded. An 
>>>> upgraded client always has the *option* of re-registering itself 
>>>> and getting a new client_id.
>>>> I think the concern here is that rotation of client credential is 
>>>> not something discussed before. Before we put it in the spec we 
>>>> should consider the reasons for doing it and what problems it solves.
>>>> I think this may be just a case of letting people exchange 
>>>> credentials for whatever reason they feel is appropriate.  The 
>>>> version upgrade thing suggests that when a client is upgraded it 
>>>> should go to the registration server to "re-register".  Depending 
>>>> on the policy of the server, it may (or may not) receive a new 
>>>> client_id and/or new credential.
>>>> One of the best benefits I can think of is if you discover a 
>>>> version of a client has a problem, being able to select a group of 
>>>> clients by software and version is important. Thus if client_id 
>>>> doesn't trace to a particular software and version, that makes it 
>>>> hard to do.  I  think you talked about this as an issue for Blue 
>>>> Button+
>>>> Again, RFC 6749 defines no client instances or groups of clients, 
>>>> therefore I believe that it’s inappropriate to do so here.  We 
>>>> don’t need to boil the ocean.  If a new charter item is approved to 
>>>> do work on client instances and protocol elements to use and 
>>>> express them, that’s the time for the working group to consider 
>>>> that possibility – not as part of Dynamic Client Registration.
>>>>     4.  What is the registration access token? Why is is used? What
>>>>     is its life-cycle?  When is it issued, when is it changed? When
>>>>     is it deleted?
>>>>     See the response above above and the definition in §1.2:
>>>>         Registration Access Token: An OAuth 2.0 Bearer Token issued
>>>>         by the Authorization Server through the Client Registration
>>>>         Endpoint which is used by the Client to authenticate itself
>>>>         during read, update, and delete operations. This token is
>>>>         associated with a particular Client.
>>>>     If this can be clarified, I welcome text suggestions.
>>>> The latter part of 1.2 didn't seem like terminology but rather 
>>>> architecture or part of the introduction that describes what the 
>>>> spec does. The third point doesn't seem to fit with the other two 
>>>> except to say that the dynamic registration endpoints use their own 
>>>> access tokens called registration access tokens.
>>>> Client Registration Endpoint: The OAuth 2.0 Endpoint through which
>>>>        a Client can request new registration.  The means of the Client
>>>>        obtaining the URL for this endpoint are out of scope for this
>>>>        specification.
>>>>     o  Client Configuration Endpoint: The OAuth 2.0 Endpoint through
>>>>        which a specific Client can manage its registration information,
>>>>        provided by the Authorization Server to the Client.  This URL for
>>>>        this endpoint is communicated to the client by the Authorization
>>>>        Server in the Client Information Response.
>>>>     o  Registration Access Token: An OAuth 2.0 Bearer Token issued by the
>>>>        Authorization Server through the Client Registration Endpoint
>>>>        which is used by the Client to authenticate itself during read,
>>>>        update, and delete operations.  This token is associated with a
>>>>        particular Client.
>>>> This section is meant to just introduce the new terms that are then 
>>>> explained in greater detail throughout the rest of the document. 
>>>> Yes, it's a bit architecture, but only in the sense that you need 
>>>> to define the terms that make up your architecture. How would you 
>>>> suggest that it change?
>>>> Probably this is more a matter of style.  But, what happened for me 
>>>> is I naturally skipped the terminology section, as I wasn't 
>>>> expecting protocol components to be there.  "terminology" is 
>>>> something I think people tend to use as a dictionary rather than as 
>>>> protocol component description.  Maybe the chairs can advise?
>>>>     If we distinguish between first time registration of a
>>>>     particular client software package, it is possible that
>>>>     somethings like authentication method can be negotiate in or
>>>>     out-of-band at that time. Subsequent registrations should only
>>>>     have parameters for items that could change per deployment
>>>>     (like tos_uri).  I think token_endpoint_auth_method is one
>>>>     thing that should not be negotiated per instance.
>>>>         When subsequent instances register, I have to ask the
>>>>         question, for example when would things like
>>>>         "token_endpoint_auth_method" be negotiated or be different
>>>>         for the same client software? Should not all instances use
>>>>         the same authentication method.
>>>>     I'm confused by this -- as far as the dynamic registration spec
>>>>     is concerned, all instances are separate from each other. All
>>>>     parameters change per instance. And instance, you should keep
>>>>     in mind, is defined as any one copy of the client code
>>>>     connecting to any new authorization server. That pairing
>>>>     creates the client_id, and therefore the instance, and
>>>>     therefore the registration access token, and therefore the
>>>>     registration itself at a conceptual level. So there is no way
>>>>     other than per-instance for a client to ask for a particular
>>>>     token_endpoint_auth_method. Where else would the AS find out
>>>>     about it?
>>>> We still disagree on this. It is my assertion that clients should 
>>>> NEVER ask for a particular token auth method. Since it is the AS 
>>>> that is authenticating the client, then it is the AS's right to set 
>>>> the authentication policy.  The role of dynamic reg endpoint is to 
>>>> inform the client what it must do.  My assumption is that during 
>>>> the first time a piece of software is registered (the first 
>>>> instance), there could be some OOB discussion by an administrator 
>>>> to approve the particular authentication type for the AS in question.
>>>> I haven't heard a reason justifying this parameter other then "it 
>>>> is needed".  Why?
>>>> The role of the dynamic registration protocol is twofold: half of 
>>>> that is the server informing the client what it must do. But the 
>>>> other half is the client informing the server what it *can* do, or 
>>>> what it *wants* to do.
>>>> And again, there's no way to distinguish a first instance from a 
>>>> subsequent instance unless you're doing something in addition. 
>>>> Nothing is stopping the same application from registering a new 
>>>> instance of itself for every single user or every single token that 
>>>> it wants to get access for. That's complicated and wasteful and not 
>>>> a great idea, sure, but  there's no useful way to prevent that kind 
>>>> of behavior if you also want open registration of clients.
>>>> I think we've discussed how recognizing subsequent instances is 
>>>> easily done.
>>>> As I mentioned in the other thread, if a developer chooses to limit 
>>>> the capabilities of the client it must do so by looking to the 
>>>> developer or standard behind the API.  Otherwise they are taking 
>>>> the chance.  There's no way a developer can query all the potential 
>>>> deployers to ask what authn types will you use. As I said, the net 
>>>> effect in the absence of an API standard dictating what should be 
>>>> supported, the developer will have to implement all methods.
>>>> My point here is that none of this is helped by the client app 
>>>> saying what it supports. A developer who takes the route of 
>>>> limiting implementation takes the chance that the server will not 
>>>> accept.  So why negotiate within registration?
>>>>     And there's no way other than per-instance for the server to
>>>>     tell the client which token_endpoint_auth_method to use. All
>>>>     instances will probably ask for the same
>>>>     token_endpoint_auth_method from all auth servers they talk to,
>>>>     right? And each AS will tell each instance that registers with
>>>>     it to use a particular auth method. There is no way to tie
>>>>     together different instances across (or within) auth servers
>>>>     without specifying a significant amount of other machinery.
>>>>     Which is not to say that it's not useful in some circumstances
>>>>     to tie together different instances of the same code across (or
>>>>     within) auth servers. This is why, with Blue Button+, we
>>>>     specified a specific token format for the initial access token
>>>>     that the clients use to call the registration endpoint the
>>>>     first time,  as well as a discovery protocol against a
>>>>     centralized server that handles pre-registration. All of this
>>>>     machinery is, in my opinion, a stupendous overkill for the
>>>>     general case, though if some folks find use for it outside of
>>>>     BB+ then it'd be a good thing to abstract out and make its own
>>>>     spec that extends the Dyn Reg spec in a fully compatible way.
>>>>     Furthermore, even in Blue Button+ we specify that all auth
>>>>     servers MUST also accept open registration, without an initial
>>>>     access token, where the client simply shows up and says "hey,
>>>>     here are my parameters." The auth server has no way to know in
>>>>     this case any kind of out-of-band negotiation for different
>>>>     things. In BB+ we are writing very specific policy guidelines
>>>>     about how to present the UX and things to the end user for all
>>>>     of these different cases. But again, all of this is specific to
>>>>     the BB+ use case, and I don't see value in dragging it in to
>>>>     the registration spec on its own. I believe it would be far too
>>>>     limiting.
>>>>     See my previous comments on differentiating client instances
>>>>     being out of scope without rechartering to do this new work and
>>>>     on what the registration_access_token is.  In short, the
>>>>     registration_access_token is an RFC 6750 bearer token issued to
>>>>     the party registering the client, enabling it to subsequently
>>>>     retrieve information about the client registration and to
>>>>     potentially update the registration information for that
>>>>     registered client. Again, I’ll work with Justin to make sure
>>>>     that this is as clear as possible in the specification.
>>>>     Finally, there seems to be an inconsistent style approach with
>>>>     draft-hardjono-oauth-resource-reg
>>>>     <> which
>>>>     uses ETags. Should this draft do so as well?
>>>>     That's an individual submission, not a working group draft.
>>>>     Nobody has, until now, even mentioned the use of ETags here.
>>>>     UMA (where the resource registration draft comes from) uses
>>>>     ETags, hence their inclusion there. I personally don't see
>>>>     their utility here, though, and I wouldn't want to include a
>>>>     wholly new mechanism this late.
>>>> Yes. Thomas' draft is not a WG document. But that doesn't mean he 
>>>> doesn't have a point. It's worth discussing.
>>>> One could argue that the point of an ETag is that it is useful for 
>>>> change detection when there are multiple writers to a particular 
>>>> resource.  In the design of dynamic registration endpoint, there 
>>>> should only be one writer -- the client. This is an important 
>>>> observation.
>>>> There are other mechanisms that handle this -- namely, the 
>>>> registration access token and the client_id. Many instances include 
>>>> the client_id in some form in the client configuration endpoint's 
>>>> URL for sanity checking, as described in §4.1.
>>>> If everyone agrees, I'm in agreement. But it will likely mean 
>>>> changes for the resource reg draft if adopted.
>>>> ETags seem like an unnecessary addition (and potential 
>>>> complication) to the specification. It’s already working fine as-is.
>>>>     */Specific items:/*
>>>>     ---------------------
>>>>     *"token_endpoint_auth_method"*
>>>>     There is some confusion as to whether this applies to server or
>>>>     client authentication.  Suggest renaming parameter to
>>>>     "token_endpoint_client_auth_method"
>>>>     This is the first I've heard of this particular confusion. I'm
>>>>     fine with either name but at this stage I don't want to make
>>>>     syntax changes without very, very compelling reasons to do so.
>>>> The question was raised to me by some new developers. It seems 
>>>> obvious to us as experienced OAuth persons, but to new developers 
>>>> it seems unclear.  Also, now that you are introducing registration 
>>>> authentication, the whole thing gets very confusing. So it is 
>>>> useful disambiguate all the parameters where possible.  That said, 
>>>> I wouldn't mind shorter names (maybe not quite as short as the JOSE 
>>>> stuff ;-)
>>>> Fair enough, but again, I only want to do syntax changes if the 
>>>> rest of the WG *really* wants to.
>>>> I agree with Justin here.  I’m fine clarifying the description of 
>>>> this parameter to resolve the potential ambiguities that you cite, 
>>>> Phil.  I’m not OK revising the syntax without a compelling reason 
>>>> to do so.
>>>>     * Currently, the API only supports a single value instead of an
>>>>     array.  If the purpose is to allow the client to know what auth
>>>>     methods it supports, this should be an array indicated what
>>>>     methods the client supports - or it should not be used.
>>>>     I would rather like this to be an array, personally, and
>>>>     brought it up with the OpenID Connect working group about six
>>>>     months ago. But there it was decided that a single value was
>>>>     simpler and sufficient for the purpose. The IETF draft has
>>>>     inherited this decision. I *believe* (though am not 100%
>>>>     positive) that I brought up this very issue in the WG here but
>>>>     didn't receive any traction on it, so single it remains.
>>>> I can get behind multiple values. In this case, it changes the 
>>>> meaning of the parameter. Instead of the client forcing the server 
>>>> to use a particular method, the client is informing the server 
>>>> about what methods it can perform. This allows the server to assign 
>>>> the appropriate method based on its own policy.
>>>> Also note that this field, like all others in §2, represents two 
>>>> things: the client telling the server "I want to use this value for 
>>>> this field", and the server telling the client "this is the value 
>>>> you have for this field". It's not exactly a negotiation, more like 
>>>> making a polite request to an absolute dictator who has the last 
>>>> word anyway. But at least this dictator is nice enough to tell you 
>>>> what their decision was instead of just decapitating you.
>>>> This is the heart of my objection. This fuzziness is is going to 
>>>> lead to interop issues.
>>>> There is no fuzziness that I can see here. It's parallelism between 
>>>> what goes in to the endpoint and what comes out of it. The 
>>>> semantics for the request and the response are different, and 
>>>> differentiable by the fact that one is a request and the other is a 
>>>> response.
>>>> The inter-op issue I would like to point out is that the spec does 
>>>> not currently specify if particular input values are singular or 
>>>> multiple.  If an implementer assumes singular and clients assume 
>>>> multiple, we have issues.
>>>> The multiple/single discussion above gets to the heart of what I 
>>>> **do** believe is a deficiency in the specification, as it’s 
>>>> currently written.  The authors, myself included, have failed to 
>>>> make it 100% clear that discovery of Authorization Server 
>>>> functionality is out of scope for this specification. I strongly 
>>>> believe that we need to add a clear statement to this effect in the 
>>>> introduction to the specification.
>>>> The purpose of the Dynamic Client Registration specification is for 
>>>> the client to register with the Authorization Server and to inform 
>>>> it of properties of the client that the AS may want/need to be 
>>>> aware of.  It **is not** the purpose of this specification for it 
>>>> to be used by clients in any manner to discover features of the 
>>>> Authorization Server. That should be explicitly out of scope.
>>>> Currently, clients are instructed by RFC 6749 to discover 
>>>> information about Authorization Servers they interact with by 
>>>> consulting the “service documentation” (RFC 6749, Sections 3.1 and 
>>>> 3.2).  They can also learn information about Authorization Servers 
>>>> in specific contexts through discovery protocols such as OpenID 
>>>> Connect Discovery 
>>>> ( and UMA 
>>>> Discovery (TBD).
>>>> I suspect that at some point, someone in the OAuth working group 
>>>> will propose developing a generic OAuth discovery mechanism, which 
>>>> will lead to a rechartering to include this work in the working 
>>>> group’s set of deliverables.  I would support doing this work and 
>>>> the necessary rechartering to do so.
>>>> That being said, I strongly oppose trying to shoehorn piecemeal 
>>>> aspects of discovery into the Dynamic Client Registration 
>>>> specification.  It is distinct functionality and deserves 
>>>> first-class and separable treatment by the working group.  
>>>> Discovery is for potential clients to learn properties of the AS 
>>>> before registration.  Registration is for potential clients to 
>>>> inform the AS of its properties, creating a registered client.  
>>>> Discovery sends information about the AS to the Client.  
>>>> Registration sends information about the Client to the AS.  That’s 
>>>> a clean separation.  We should strongly resist muddying the two 
>>>> functions.
>>>> OAuth 2.0 is a success because it didn’t try to boil the ocean.  It 
>>>> specified how to do one thing well in a simple, web-friendly 
>>>> manner.  We should do the same – focusing on specifying 
>>>> interoperable dynamic client registration, while making it clear 
>>>> that this is distinct from discovery about Authorization Server 
>>>> properties, and making it clear that discovery is out of scope for 
>>>> this work.
>>>> I apologize at this point on behalf of myself and the other spec 
>>>> editors for not being 100% clear that discovery functionality is 
>>>> explicitly out of scope for Dynamic Client Registration.  If we had 
>>>> done so, I’m sure that many of the current questions and confusions 
>>>> would not have arisen.  I think we’d assumed that this was obvious, 
>>>> but from the current discussions, it’s apparent that it’s not 
>>>> obvious.  I will personally commit to clarifying the specification 
>>>> at this point to eliminate this potential point of confusion.
>>>> Getting back to the specifics, the only useful purpose of a 
>>>> multi-valued “token_endpoint_client_auth_method” member would be to 
>>>> enable the client to discover information about the authentication 
>>>> methods supported by the AS after the registration had been 
>>>> performed.  But that is a discovery function, and so should be part 
>>>> of the discovery work – not this specification.  We should resist 
>>>> shoehorning in bits of discovery into this specification.  It 
>>>> **is** a worthwhile topic, but deserves full consideration by the 
>>>> working group in its own right. Therefore, this member must remain 
>>>> single-valued, and be clearly specified as the method by which a 
>>>> client informs the AS which token endpoint authentication method it 
>>>> will use.  Anything else would be scope creep, and result in an 
>>>> unnecessarily complicated specification and unnecessarily 
>>>> complicated clients.
>>>>     * There is no authn method for "client_secret_saml" or
>>>>     "private_key_saml".
>>>>     Nobody has really asked that these two be included or
>>>>     specified. The extension mechanism (using an absolute URI)
>>>>     would allow someone else to define these. Is the definition in
>>>>     the SAML Assertion draft sufficient for their use?
>>>> I think this is coming from the fact that there is a JWT bearer 
>>>> draft and a SAML bearer draft.  The truth is you are defining an 
>>>> authentication that isn't even defined.
>>>>         /There are no profiles referenced or defined for
>>>>         "client_secret_jwt" or "private_key_jwt". Neither of the
>>>>         JWT or SAML Bearer drafts referenced cover these types of
>>>>         flows. They only cover bearer flows.  "client_secret_jwt"
>>>>         and "private_key_jwt" seem to have some meaning within
>>>>         OpenID Connect, but I note that OIDC does not fully define
>>>>         these either./
>>>>         The JWT assertion draft does say how to use a JWT for
>>>>         client authentication, and the DynReg text differentiates
>>>>         between a client signing said JWT with its own secret
>>>>         symmetrically vs. a client using its own private key,
>>>>         asymmetrically.
>>>>     Actually my interpretation is the JWT draft assumes the JWT
>>>>     Bearer is a bearer token.  The assumption is that if a client
>>>>     has the assertion it has the right to present it.  IOW. The JWT
>>>>     Bearer Draft is most definitively not a JWT HoK Draft.  :-)
>>>>     Regardless, you are introducing a new profile which is undefined.
>>>> I think I see the point that you're making now, let me try to 
>>>> re-state it:
>>>> While the basics of "how to present a JWT as a client credential" 
>>>> is defined here: 
>>>> it's not completely specified in that it doesn't fully restrict the 
>>>> signature secret source, the audience claim, and other things that 
>>>> the AS would need to check and validate. Right? The dynamic 
>>>> registration draft can define those cases in greater detail if 
>>>> needed (though I think it does so sufficiently as-is, I welcome 
>>>> more clarity).
>>>> I'd be OK with adding the SAML bit, going into greater detail on 
>>>> the JWT bits, or dropping the JWT bits, if the WG wants to do any 
>>>> of those actions. My objection is that the JWT stuff is already in 
>>>> use and functioning and it'd be a shame to leave it out.
>>>> I guess then the mistake the JWT Bearer and SAML Bearer drafts 
>>>> authors made is they assumed everyone had the same definition of 
>>>> bearer token.  To me a bearer token opaque to the client. It 
>>>> therefore cannot do any signature work with regards to the token 
>>>> itself.  Now, that's not to say a proof didn't occur between the 
>>>> client and the token issuer, but when the client wields the token, 
>>>> it is handling an opaque string.
>>>> The concept of client_secret_jwt suggests an HoK profile. 
>>>>  Therefore of course the bearer drafts are a little underspecified 
>>>> when it comes to HoK profiles.
>>>> So for example, you need a draft like the MAC draft for this.
>>>> I'm having trouble overall here. It seems the authn types suggest 
>>>> ONLY strong authentication for clients, yet during the registration 
>>>> process the current draft isn't able to correlate multiple 
>>>> instances of the same software (even in a self-asserted way).  If 
>>>> you haven't authenticated the software at all, why have strong 
>>>> client auth?
>>>>             There is no authentication method defined for
>>>>             "client_bearer_saml" or "client_bearer_jwt" or
>>>>             "client_bearer_ref".  Since the bearer specs say this
>>>>             is acceptable,  the dynamic registration spec should
>>>>             accept these.
>>>>             I don't understand this bit -- where are these defined
>>>>             in RFC6750? I don't even know what client_bearer_ref
>>>>             would refer to.
>>>>         6750 says you can use a bearer assertion (e.g. obtained
>>>>         from an IDP) and wield it as an authentication assertion.
>>>>          The client is NOT creating or modifying the assertion. The
>>>>         client is simply passing one it previously obtained.
>>>>         What you are describing is not bearer. It is holder of key.
>>>>         Very very different.
>>>>         A possible suggestion is to remove client_secret_jwt and
>>>>         private_key_jwt and define those as register extensions
>>>>         since these profiles are not defined.
>>>>         That's possible, but they are in active use already.
>>>>         That may be true. But then you need to write another draft
>>>>         so the rest of us can implement it in an interoperable way.
>>>>          Me I prefer not to guess what you are doing.
>>>>     This much I agree with.
>>>>     Justin, John, and I discussed this issue and agree with your
>>>>     suggestion, Phil. Since they are not completely specified, we
>>>>     will remove the client_secret_jwt and private_key_jwt methods
>>>>     from the specification and add a registry, enabling
>>>>     specification that do fully specify these and other token
>>>>     endpoint authentication methods, including potential methods
>>>>     using SAML assertions, to register them in the registry, rather
>>>>     than trying to bake them into the Dynamic Client Registration
>>>>     specification.
>>>>         *About "tos_uri" and "policy_uri"*
>>>>         The distinction between tos_uri and policy_uri is unclear.
>>>>          Can we clarify or combine them?
>>>>         Terms of service and policy are two different documents.
>>>>         One is something that a user accepts (generally describing
>>>>         what the user will do), one is a statement of what the
>>>>         service provider (in this case, the client) will do. More
>>>>         importantly, we used to have only one, and several people
>>>>         asked for them to be split.
>>>>     Several developers were confused by this. In particular they
>>>>     couldn't figure out which was used for what.  Just passing
>>>>     along the feedback.
>>>>     OK, the distinction that I see is that the TOS is contractual,
>>>>     the Policy is a statement. Re-reading the definitions in there
>>>>     right now, that can be made much clearer. (It even looks like
>>>>     some OIDC text leaked into the definition of policy_uri and
>>>>     that hadn't been caught yet.)
>>>>     I support clarifying the language on these definitions, and
>>>>     will work with Justin to do so.
>>>>         Also, aren't these really URIs or are they meant to be URLs?
>>>>         There was already discussion about this on the list: The
>>>>         IETF is apparently trying to deprecate URL in favor of URI
>>>>         in new specs. So in practice they'll nearly always be URLs,
>>>>         but since all URLs are URIs we're not technically incorrect
>>>>         in following the new policy. And it makes the IESG less mad
>>>>         at us, which is a plus.
>>>>     Arg. Nice.  Then the text should say the value passed must
>>>>     resolve to a valid web page, document, whatever.
>>>>     That's fair, and it's something that the AS can even check if
>>>>     it wants to.
>>>>     Agreed on this clarification.
>>>>         *About "jwks_uri"*
>>>>         A normative reference for
>>>> is
>>>>         needed.
>>>>         Yes, you're correct, I'll add that.
>>>>         Should be URL instead of URI?
>>>>         See above. :)
>>>>         Agreed on adding this reference.
>>>>         *Section 2.1*
>>>>         In the table urn:ietf:params:oauth:grant-type:jwt-bearer
>>>>         is missing.
>>>>         It's there in the copy of -10 I'm reading off
>>>>         <>right now … ?
>>>>     '
>>>>     Sorry I meant: urn:ietf:params:oauth:grant-type:saml-bearer
>>>>     Ah, that makes more sense. If the WG wants to add in SAML
>>>>     support to parallel the JWT support, I'd be OK with that.
>>>>         “As such, a server supporting these fields SHOULD take
>>>>         steps to ensure that a client cannot register itself into
>>>>         an inconsistent state.”
>>>>         We may want to define more detailed HTTP error
>>>>         response. E.g. 400 status code + defined error code
>>>>         (“invalid_client_metadata”)?
>>>>         I'd be fine with defining a more explicit error state in
>>>>         this case. I think it would help interop for the servers
>>>>         that want to enforce grant-type and response-type
>>>>         restrictions, but servers that can't or don't care about
>>>>         restricting grants types and whatnot don't have to do
>>>>         anything special.
>>>>         I **think** that this goes away with the deletion of
>>>>         client_secret_jwt and private_key_jwt in favor of the
>>>>         registry…  I’ll do a consistency check and verify that when
>>>>         the spec is updated accordingly.
>>>>         *Section 2.2*
>>>>         May want to add:
>>>>         When “#” language tag is missing, (e.g. “#en” is missing in
>>>>         “client_name”, instead of “client_name#en”) the OAuth
>>>>         server may use interpret the language used based on server
>>>>         configuration or heuristics.
>>>>         That seems inconsistent with what we already have:
>>>>             If any human-readable field is sent without a language
>>>>             tag, parties using it MUST NOT make any assumptions
>>>>             about the language, character set, or script of the
>>>>             string value, and the string value MUST be used as-is
>>>>             wherever it is presented in a user interface.
>>>>         Which is to say, treat it as a raw byte-value-string and
>>>>         don't try to get fancy.
>>>>     I will discuss with our developers. I'm not sure the as-is works.
>>>>     Is it the intent that when the client has localized
>>>>     "client_name" for example, it should pass all language
>>>>     variations in a JSON array?
>>>>     Or, should part of the registration be to indicate which
>>>>     interface language the client wishes to use?  Then it only
>>>>     passes a single value for that registration?
>>>>     No, the client should pass parameters as multiple separate
>>>>     values. Connect has this in its example:
>>>>         "client_name": "My Example",
>>>>         "client_name#ja-Jpan-JP":
>>>>           "クライアント名",
>>>>     Should we add that to at least one of the examples in DynReg?
>>>>     (The language tags are a late addition, so the examples don't
>>>>     reflect it.)
>>>> An example would definitely help.
>>>>     If the client passes only a single unadorned field, the AS
>>>>     can't make any assumption about what language it is. Think of
>>>>     this as the internationalized value of the field while the
>>>>     language tags are the localized versions of the field. This is
>>>>     why we recommend that the bare-value always be sent by the
>>>>     client, so that in the lack of anything more specific, the AS
>>>>     can at least do *something* with it.
>>>>     Passing in a "default" language field (like default_locale or
>>>>     the like) is only going to lead to pain for implementors of
>>>>     both clients and servers, and it's going to hurt the
>>>>     interoperability of the human-readable fields.
>>>> I think what I meant is since you are allowing each client to 
>>>> register different things, AND the client likely already knows the 
>>>> user's preferred language, why wouldn't the client just pass text 
>>>> values in one language and another parameter indicating preferred 
>>>> language in the case of any service generated text.
>>>> Is the reason you are passing multiple localizations is so that you 
>>>> can use the preferred language of the resource owner rather then 
>>>> the client user? I wonder if that is correct.  If the language 
>>>> preferences are in fact different, what would the user of the 
>>>> client app expect?
>>>> ----> any multi-lingual people have any opinions here?
>>>>     Without specific proposed text changes to review, it’s hard to
>>>>     know what to think about this comment.  Unless a specific
>>>>     proposed text change is sent to the list with clear rationale
>>>>     for why it’s better than what’s there now and reviewed by the
>>>>     working group, I don’t believe we should change the
>>>>     specification in response to this comment.
>>>>         *Section 3*
>>>>         Existing text:
>>>>         “In order to support open registration and facilitate
>>>>         wider interoperability, the Client Registration
>>>>         Endpoint SHOULD allow initial registration requests with
>>>>         no authentication.  These requests MAY be rate-limited or
>>>>         otherwise limited to prevent a denial-of-service attack on
>>>>         the Client Registration Endpoint.”
>>>>         I would suggest to change the first “SHOULD” to “MAY”.   In
>>>>         most cloud services, the first client is registered by a
>>>>         human user. Then, other clients can be further used to
>>>>         automate other client registration.  So, the first request
>>>>         would typically come with an authenticated user identity.
>>>>         I think the weight of "SHOULD" is appropriate here, because
>>>>         I believe that turning off open registration at the AS
>>>>         (which is what this is talking about) really ought to be
>>>>         the exception rather than the rule.
>>>>     I think you are reading it wrong -- a double-negative issue.
>>>>     The end of the sentence is "no authentication".  You are
>>>>     implying that NO Authentication us what should normally be
>>>>     done. I think you intend anonymous authentication to be the
>>>>     exception rather than the rule don't you?
>>>>     No, I think that anonymous authentication should be the rule.
>>>>     Open registration should be default.
>>>> I disagree.  Again,  the spec seems contradictory. It suggests 
>>>> strong client auth methods and at the same time anonymous 
>>>> registration.  Yes you gain uniqueness, but that's about it.
>>>>     On the flip side, the earlier paragraph:
>>>>     “The Client Registration Endpoint MAY accept an initial
>>>>     authorization credential in the form of an OAuth 2.0 [RFC6749]
>>>>     access token in order to limit registration to only
>>>>     previously authorized parties. The method by which this access
>>>>     token is obtained by the registrant is generally out-of-band
>>>>     and is out of scope of this specification.”
>>>>     I tend to think it would be better to change this “MAY” to
>>>>     “SHOULD”.
>>>>     That access token would carry a human user
>>>>     authenticated identity somehow. In some cases, it can be a pure
>>>>     authenticated user assertion token.
>>>>     Again, disagree, for the same reasoning as above.
>>>> Same reasoning.
>>>> I agree with Justin here.  The default should be that open 
>>>> registrations are enabled. The exception case is that specific 
>>>> permissions are required to perform dynamic client registration.
>>>> *About section 4.3:*
>>>> If the client does not exist on this server, the server MUST respond
>>>>     with HTTP 401 Unauthorized, and the Registration Access Token used to
>>>>     make this request SHOULD be immediately revoked.
>>>> If the Client does not exist on this server, shouldn't it return a 
>>>> "404 Not Found"?
>>>> If revoking the registration access token, is it bound to a single 
>>>> client registration?  This is not clear.  What is the lifecycle 
>>>> around registration access token? Only hint is in the Client 
>>>> Information Response in section 5.1.
>>>> The language about the 401 here (and in other nearby sections) is 
>>>> specifically so that you treat a missing client and a bad 
>>>> registration access token the same way. You see, returning a 404 
>>>> here actually indicates things were in an inconsistent state. 
>>>> Namely, that the registration access token was still valid but the 
>>>> client that the registration access token was attached to doesn't 
>>>> exist anymore. The registration access token in meant to be tied to 
>>>> a client's instance (or registration), so it's actually more 
>>>> sensible to act as though the registration access token isn't valid 
>>>> anymore. In at least some implementations (specifically ours at 
>>>> MITRE that's built on SECOAUTH in Java), you'd never be able to 
>>>> reach the 404 state due to consistency checking with the inbound token.
>>>> Since the intent of the registration access token is that it's 
>>>> bound to a single instance, its lifecycle is generally tied to the 
>>>> lifecycle begins at the issuance of a new client_id with that 
>>>> instance. That token might be revoked and a new one issued on Read 
>>>> and Update requests to the Client Configuration Endpoint (and the 
>>>> client needs to be prepared for that -- same as the client_secret), 
>>>> and it will be revoked when the client is deleted either with a 
>>>> Delete call to the Client Configuration Endpoint or something 
>>>> happening out-of-band to kill the client.
>>>> Should we add more explanatory text to the definition in the 
>>>> terminology section? Elsewhere? I'm very open to concrete 
>>>> suggestions with this, since I don't think it's as clear as we'd like.
>>>> I think we should look at it.
>>>> For security reasons, it’s generally not good to distinguish 
>>>> between “not found” and “unauthorized” errors in responses, as that 
>>>> can provide the attacker an oracle to probe whether a particular 
>>>> entity exists  I don’t think a change is called for here.
>>>> *About section 5.1:*
>>>> Is registration_access_token unique?  Or is it shared by multiple 
>>>> instances? If shared, then registration_access_token can't be 
>>>> revoked on delete of client.
>>>> The registration_access_token is unique to a registered client, in 
>>>> the RFC 6749 sense of “client”. Again, if we want to do work on 
>>>> “client instances”, we need to recharter and take this distinct 
>>>> work item up explicitly.
>>>> Suggest rename “expires_at” to “client_secret_expires_at”,
>>>> Suggest to rename “issued_at” to “id_issued_at”
>>>> While I do like the suggestion of changing these to 
>>>> client_secret_expires_at and client_id_issued_at, and I think these 
>>>> are more clear and readable,
>>>> I don't want to change the syntax during last call unless there is 
>>>> a clear need and a clear consensus for doing so.
>>>> That's why we are having last call. To confirm consensus on the draft.
>>>> Same reasoning as earlier. You now have multiple tokens 
>>>> (registration access and client) in play. The spec needs to be 
>>>> clear which one it is talking about.
>>>> I'm fine with the suggested change but I would like more feedback 
>>>> from other people before moving forward with it. There's a lot of 
>>>> value in "just pick a name and ship it" as well though, and I don't 
>>>> want to devolve into bike shedding. (I'm not accusing you of bike 
>>>> shedding quite yet, btw, just afraid of getting into a long debate 
>>>> on names.)
>>>> Again, this was a problem raised by people new to the 
>>>> specification. They found it confusing. I tend to agree. We're not 
>>>> talking about what colour to paint the shed. We're talking about 
>>>> whether the bike shed is a house.  :-)
>>>> I'm not too fussed about whether you call it "cl_sec_expiry" or 
>>>> "client_secret_expires_at".
>>>> If the definitions of “expires_at” or “issued_at” are unclear, we 
>>>> should clarify them.  If you believe that this is the case Phil, 
>>>> can you supply proposed alternative definition text that is 
>>>> clearer?  That being said, I believe that at this point we should 
>>>> stick with the existing protocol element names unless overwhelming 
>>>> working group sentiment emerges to change them.  They are already 
>>>> working fine as-is in production deployments.
>>>>     *Section 7*
>>>>     When a client_secret expires is it the intent that clients do
>>>>     an update or refresh to get a new client secret?
>>>>     Yes, the client is supposed to either call the read or update
>>>>     methods on the client configuration endpoint to get its new
>>>>     secret. As discussed above, I'm not sure that's as clear as it
>>>>     needs to be, and I welcome suggestions on how to clarify this.
>>>>     Either is a reasonable behavior on the behalf of clients,
>>>>     depending upon context.  I support adding text to clarify this.
>>>>     Again, thanks for the very thorough read through. Have you
>>>>     implemented any of the spec yet, either as-is or with any of
>>>>     your suggested changes?
>>>> Yes. Much of the feedback is coming from our development community.
>>>> Ah, very cool. Developer experience is the most valuable feedback, 
>>>> in my opinion. If you can't actually build the blasted thing, what 
>>>> good is it? :)
>>>> Glad to hear that you’re working with developers building the 
>>>> spec.  Please thank them for the feedback.
>>>>  -- Justin
>>>> Best wishes,
>>>> -- Mike
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