Re: [OAUTH-WG] Transaction Tokens issuance in the absence of incoming token

[Dmitry Telegin <[e-mail]>]

Hello Atul,

As an alternative to Token Exchange and separate (new) endpoint, have you
ever considered OAuth 2.0 Extension Grants
<https://datatracker.ietf.org/doc/html/rfc6749#section-4.5>? This could
give us more flexibility as will let us define our own set of input
parameters and validation rules (opposite to Token Exchange that restricts
us to subject_token and friends).

Regards,
Dmitry

On Thu, Apr 4, 2024 at 11:02 PM Atul Tulshibagwale <[e-mail]> wrote:

> Thanks very much for your feedback, Joe!
>
> On Wed, Apr 3, 2024 at 10:16 AM Joseph Salowey <[e-mail]> wrote:
>
>> Hi Atul,
>>
>> I'm just starting to review the transaction tokens draft and have only a
>> minimal understanding of the token exchange document at this point so I'm
>> lacking a little background, but I have a few comments and questions below.
>>
>> On Fri, Mar 29, 2024 at 10:39 AM Atul Tulshibagwale <[e-mail]> wrote:
>>
>>> Hi all,
>>> We had a meeting today (notes here
>>> <https://hackmd.io/@rpc-sec-wg/HJNXYKkk0>) in which we discussed the
>>> question of what we should do if there is no incoming (external) token in
>>> the request to issue a Transaction Token
>>> <https://datatracker.ietf.org/doc/draft-ietf-oauth-transaction-tokens/>
>>> (TraT). We identified a few circumstances under which this can happen:
>>>
>>>    - The requesting service is triggered by a non-OAuth based flow such
>>>    as email or an internal trigger
>>>    - The client of the requesting service uses means other than an
>>>    access token to authorize the call (e.g. MTLS)
>>>
>>> [Joe] I think there will be a fair number of systems that support means
>> of authorizing non-oauth flows.
>>
>>
>>
>>> We identified a few possibilities listed below. Please note that the
>>> Transaction Tokens draft assumes that the TraT Service trusts the
>>> requesting service, so all the possibilities below assume this.
>>>
>>>
>> [Joe] yes, you are trusting another part of the system to perform some
>> authorization and inform the token service of the result.
>>
>>
>>> Here are some possibilities we discussed:
>>>
>>>    1. *Request Details*: Put the subject information in the
>>>    request_details parameter of the TraT request, and the subject_token value
>>>    is set to "N_A"
>>>    2. *Self-Signed Token*: The requester generates a self-signed JWT
>>>    that has the subject information and puts that in the subject_token value
>>>
>>> [Joe] I like having signed tokens, but if this is really information
>> just exchanged between two endpoints it may be more work than necessary.
>>
>>>
>>>    1. *Separate Separate Endpoint*: The TraT service exposes a separate
>>>    endpoint to issue TraTs when there is no incoming token, and that endpoint
>>>    can be defined such that the request does not have a subject_token
>>>    parameter. This endpoint is not a profile of OAuth Token Exchange
>>>    2. *Separate Endpoint Only*: Extending the thought above, the
>>>    requester can always extract the content of the incoming token into the
>>>    "request_details" parameter, so why do we need the Token Exchange endpoint
>>>
>>> [Joe] What do we gain by using token exchange? While it seems that there
>> is overlap between delegation/impersonation it seems that transaction
>> tokens are sort of a superset and contain additional information about the
>> context of the transaction.   If it looks like token exchange is too
>> constraining then transaction tokens may just be a different use case.
>> With the understanding I currently have I'd either go with 4. Separate
>> Endpoint Only or 2. Self Signed token.  Splitting the endpoints could be
>> valid, but it seems a bit weird for me, if we did decide to do that then
>> probably we wouldn't need to sign the information unless the request is
>> going to traverse multiple systems.
>>
>>
>>
>>> We would like to understand how the group feels about these choices, or
>>> if you have other suggestions / thoughts on this topic.
>>>
>>> Thanks,
>>> Atul
>>>
>>> --
>>>
>>> <https://sgnl.ai>
>>>
>>> Atul Tulshibagwale
>>>
>>> CTO
>>>
>>> <https://linkedin.com/in/tulshi> <https://twitter.com/zirotrust>
>>> <[e-mail]>
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