[Openid-specs-fapi] JWT Secured Authorization Response Mode (#155)

Torsten Lodderstedt torsten at lodderstedt.net
Sat Aug 18 08:27:02 UTC 2018


I assume query.jwt only works with response type code and fragment.jwt with response type token. If so I would argue form_post.jwt and jwt would suffice as response mode values since the other encodings are determined by the combination of response type and response mode value jwt.

> Am 17.08.2018 um 15:28 schrieb Brian Campbell via Openid-specs-fapi <openid-specs-fapi at lists.openid.net>:
> 
> I like Vladimir's suggestion FWIW.  
> 
>> On Thu, Aug 16, 2018 at 9:52 PM Vladimir Dzhuvinov via Openid-specs-fapi <openid-specs-fapi at lists.openid.net> wrote:
>> How about having response_mode=jwt to indicate the standard redirect encoding (query, fragment) for the requested response type, and 
>> 
>> response_mode=form_post.jwt
>> response_mode=query.jwt
>> response_mode=fragment.jwt 
>> 
>> to set a preferred encoding explicitly?
>> 
>> The `.` was chosen as a delimiter character that is unreserved in percent encoding (RFC 3986).
>> 
>> Vladimir
>> 
>>> On 15/08/18 22:35, Brian Campbell via Openid-specs-fapi wrote:
>>> As I said (or tried to say) on the call and reiterating some of the prior
>>> email, using response mode "jwt" here is a completely viable approach but
>>> it should probably be defined as a generally applicable response mode in
>>> that case. Perhaps saying that all authorization response parameters are
>>> put as claims in the JWT as the baseline. And then note exceptions like
>>> state/s_hash (and maybe id_token) and define how they specifically are
>>> handled.  I think also that some more clarity should be provided on how the
>>> response=[jwt] and state (and any other special params) are encoded for the
>>> redirection - i.e. as query string parameters, or
>>> application/x-www-form-urlencoded in a fragment component, or as form post
>>> parameters. The draft currently implies query string but there's definitely
>>> some potential ambiguity for response type(s) like the hybrid ones that do
>>> different things by default.
>>> 
>>> In FAPI part 2 s_hash is defined as,
>>> 
>>> State hash value. Its value is the base64url encoding of the left-most half
>>> of the hash of the octets of the ASCII representation of the state value,
>>> where the hash algorithm used is the hash algorithm used in the alg header
>>> parameter of the ID Token's JOSE header. For instance, if the alg is HS512,
>>> hash the state value with SHA-512, then take the left-most 256 bits and
>>> base64url encode them. The s_hash value is a case sensitive string.
>>> 
>>> So I think that this draft needs to clarify that the alg header parameter
>>> of the response JWT is used to determine the hash algorithm rather than
>>> from the ID Token (and there won't be an ID token many times). I imagine
>>> that's what most implementations would do anyway but there's definitely
>>> room for different interpretations as it's written now. And that should be
>>> tightened up.
>>> 
>>> The s_hash in the example is misleading as
>>> "s_hash":"44D41668D199FF3D525FA357A25525D738AADF2A7B1E2C819A39E38500ABAED9",
>>> is almost certainly not a base64url encoding of the left-most half of the
>>> hash of the octets of the ASCII representation of the state value. It looks
>>> like hex.
>>> 
>>> Also should a client metadata parameter be defined to say what alg(s) to
>>> use on this response JWT? Something akin to id_token_signed_response_alg
>>> and id_token_encrypted_response_alg and id_token_encrypted_response_enc but
>>> for this response JWT.
>>> 
>>> 
>>> 
>>> 
>>> On Wed, Aug 15, 2018 at 12:36 PM Brian Campbell <bcampbell at pingidentity.com>
>>> wrote:
>>> 
>>>> [re-sending to the list as I forgot to reply-all earlier before the call]
>>>> 
>>>> Hi Torsten,
>>>> 
>>>> Yes, more text would needed around other response types because code is
>>>> the only thing described currently with others being out of scope - it
>>>> says, 'Note: The response mode "jwt" can be combined with other response
>>>> types, the respective syntax and behavior is out of scope of this draft.'
>>>> 
>>>> I'm not sure I agree that state needs special treatment. But regardless,
>>>> as a general response mode, there should be more clear definition of what
>>>> goes in the JWT and what is a normal authz response parameter and how it's
>>>> all encoded.
>>>> 
>>>> Kinder regards,
>>>> Brian
>>>> 
>>>> On Wed, Aug 15, 2018 at 7:29 AM Torsten Lodderstedt <
>>>> torsten at lodderstedt.net> wrote:
>>>> 
>>>>> Hi Brian,
>>>>> 
>>>>> the mode can easily be combined with the grant type „token" (and the text
>>>>> also sketches how). One would include the response parameter access_token,
>>>>> token_type, expires_in, and scope in the JWT. I can also add more text on
>>>>> that.
>>>>> 
>>>>> I think it makes sense to treat the state value special because it binds
>>>>> the response object to the initial transaction and can be evaluated
>>>>> _before_ the JWT is being processed. This is a security precaution.
>>>>> 
>>>>> Kind regards,
>>>>> Torsten.
>>>>> 
>>>>>> Am 15.08.2018 um 14:41 schrieb Brian Campbell via Openid-specs-fapi <
>>>>> openid-specs-fapi at lists.openid.net>:
>>>>>> As a Response Mode, I had envisioned that all the authorization
>>>>> response parameters would be passed as claims of the JWT. And would be
>>>>> applicable to any response types. Something like that would more closely
>>>>> mirror OAuth JAR. And be a more generally applicable response mode.
>>>>>> What is in this draft is more of a specialized treatment of the code
>>>>> response parameter (also state). If that's the extent of the functionality,
>>>>> it's probably more appropriate to be defined as a new response type (I know
>>>>> I suggested response mode but that was with the thinking that it'd be a
>>>>> generalized mode for encoding all the response params). Or, if response
>>>>> mode is used to signal this functionality, the mode value (and spec title)
>>>>> should probably be more true to what it is actually doing. Like
>>>>> response_mode=code_in_jwt_with_state_as_s_hash_and_other_stuff_undefined or
>>>>> just response_mode=jwt_code.
>>>>>> On Thu, Aug 9, 2018 at 10:03 AM Torsten Lodderstedt via
>>>>> Openid-specs-fapi <openid-specs-fapi at lists.openid.net> wrote:
>>>>>> Hi all,
>>>>>> 
>>>>>> please find attached the first version of the draft on the new signed
>>>>> response mode (
>>>>> https://bitbucket.org/openid/fapi/issues/155/support-authorization-and-identity).
>>>>> As this draft mirrors OAuth JAR (as already pointed out by Nat), I choose
>>>>> the name accordingly.
>>>>>> Looking forward for your feedback.
>>>>>> 
>>>>>> kind regards,
>>>>>> Torsten.
>>>>>> 
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