[Openid-specs-ab] Response types clarification

Justin Richer jricher at mitre.org
Tue Feb 21 20:41:26 UTC 2012

John, thanks for the background. This leaves me with a major question 

> That was the way we originally had it.   Later on people thought that using the OAuth multi-response type was more OAuth friendly.
> Originally if you had the scope openid:
> 1 response_type=code   both code and id_token were query encoded in the response

Maybe I'm missing something, but in the "code" flow, you don't get back 
an id_token in that response. You get back a code, and that code can be 
exchanged for an access token and an id_token, since you asked for 
something that includes the "openid" scope. From Standard, section 2.2.1:

    When supplied as the value for the response_type parameter, a
    successful response MUST include an Authorization Code as defined in
    the OAuth 2.0 specification. Both successful and error responses
    MUST be added as parameters to the query component of the response.
    All tokens are returned from the Token Endpoint. Authorization
    Servers MUST support this response_type. 
So the whole issue of query-encoding the id_token isn't even an option 
here. It *is* an option if you're asking for something akin to "code 
id_token", but that wasn't on the table. In the current spec, those are 
both defined as fragment encoded anyway.

> 2 response_type=token  both access_token and id_token were fragment encoded.
> There was no way to just get code or access_token, and no way to get just id_token.

The former, yes, there is: just don't include the "openid" scope. The 
latter, no. But if you ask for a token with just the "openid" scope and 
don't ask for any other permissions, the server *could* give you a null 
or empty or otherwise useless access token there, if it wanted to. I 
agree that if this is a real and viable use case, then it should be a 
separate kind of response_type, but I'm not seeing that right now.

> It was simpler I will give you that.
> It is a bit different from adding id_token to the token endpoint in that there is no OAuth mechanism for controlling the response from the endpoint.  I suppose the alternative would have been to add an extra parameter to the token endpoint request to say if you wanted a id_token.

No, again, that's what the scope already handles. If we didn't have a 
standardized scope value, then I'd agree with this.

  -- Justin

>>> - just using "token" instead of all combinations of id_token and token ?
>>> The response type "token" could cause the OP to return both the id_token and the access token in the fragment, which is similar to the response of the tokens endpoint. I know this would return tokens the client is potentially not interested in. But this seems to be accepptable for the code response type.
>> I actually rather like this approach. It keeps the question of whether or not you want OpenID confined to the value of the 'scope' field (that is, presence of an 'openid' value in there), and it makes serialization of the ID Token just a part of the access token output, like the code flow with the token endpoint. Of course we still have to profile how it gets encoded, but it's ultimately another field in the token output.
>> -- Justin
>>> Am 20.02.2012 20:44, schrieb John Bradley:
>>>> Response types are single values.   (I am starting to hate Erin's compromise)
>>>> The response types are documented in: http://openid.bitbucket.org/oauth-v2-multiple-response-types-1_0.html
>>>> The response types "code id_token",  "id_token token", and "code id_token token"  MUST return a id_token and the response SHOULD be fragment encoded.
>>>> Now you are asking yourself why is that SHOULD be fragment encoded as opposed to MUST be fragment encoded.
>>>> The reason for that is that the response_type registration is leaving wiggle room to use the same response type with post message as well.
>>>> For that to work the client would need to register a JS Origin and DOM Channel Names(or pick a fixed strings).  We did stub in post message configuration parameters, but removed them due to there not being a OAuth spec yet.
>>>> Probably more than the yes you were looking for, but the history provides some perspective.
>>>> John B.
>>>> On 2012-02-20, at 3:52 PM, Torsten Lodderstedt wrote:
>>>>> Hi John,
>>>>> thanks for the clarification.
>>>>> So all response types containing the string value "id_token" cause the authorization server to directly return a id_token (along with all other parameters) to the client via fragment?
>>>>> regards,
>>>>> Torsten.
>>>>> Am 20.02.2012 19:48, schrieb John Bradley:
>>>>>> Inline
>>>>>> On 2012-02-20, at 3:30 PM, Torsten Lodderstedt wrote:
>>>>>>> Hi all,
>>>>>>> I'm trying to catch up with the Implementors Draft and need some advice from the group.
>>>>>>> Is it correct that "code" is the only response type, which is delivered to the client via URI query parameter? For all other response types, the response parameters are encoded within the URI fragment.
>>>>>> Yes
>>>>>>> Furthermore, is the client always issued an access token _and_ an id_token for scope "openid" and response type "code"?
>>>>>> The response from the Authorization server is code as was asked for.
>>>>>> The Token endpoint includes id_token in it's response as an extra parameter.
>>>>>> So strictly speaking Yes id_token is always issued if the scope is 'openid'  (scope is a single value with spaces, so don't say includes) and the response_type is code.
>>>>>> However the response type is code and only code.
>>>>>> The id_token is only returned if code is exchanged at the token endpoint for and access_token and id_token.
>>>>>> So I suppose you could avoid getting id_token by not exchanging code, but I don't think anyone is going to think that is a good idea.
>>>>>> The problem is that response)type only controls what comes back from the Authorization endpoint, and not the token endpoint.
>>>>>> The only option we found was overloading a scope to change the behaviour of the token endpoint to return the extra value.
>>>>>> The token endpoint response is direct, so size is not a big issue.  It was simpler to always return it from that endpoint than create a complicated way of asking for it from the token endpoint.
>>>>>> Worst case the response is a bit bigger, but the client ignores the extra parameter.
>>>>>> John B.
>>>>>>> thanks in advance,
>>>>>>> Torsten.
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