Re: [OAUTH-WG] OAuth Security Topics -- Recommend authorization code instead of implicit

[Torsten Lodderstedt <[e-mail]>]

> Am 28.11.2018 um 23:50 schrieb n-sakimura <[e-mail]>:
> 
> That works.

Good!

I just realized this text has an issue with „token“ (only). It would allow „token“ to be used if the token would sender constrained. This completely ignores the fact implicit also shall be abandoned because of its vulnerability for access token injection. 

I therefore propose a modified text: 

   In order to avoid these issues, Clients SHOULD NOT use the implicit
   grant. Furthermore, clients SHOULD only use other response types causing the authorization server to
   issue an access token in the authorization response, if the particular response type detects access token 
   injection and the issued access tokens are sender-constrained.

Or we just state:

  In order to avoid these issues, Clients SHOULD NOT use the response type „token". The response types
„token id_token“ and „code token id_token“ SOULD NOT be used, if the issued access tokens are not 
sender-constrained.

> 
> In fact, I would further go and say MUST NOT but that probably is too much for a security consideration.
> 

Mike suggested to go with a SHOULD NOT to get the message out but give implementors time to move/change.

> Best,
> 
> Nat
> 
> Nat Sakimura / [e-mail] / [phone]
> 
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>  
> 差出人: Torsten Lodderstedt <[e-mail]>
> 送信日時: 水曜日, 11月 28, 2018 11:38 午後
> 宛先: n-sakimura
> Cc: Dick Hardt; Hannes Tschofenig; [e-mail]
> 件名: Re: [OAUTH-WG] OAuth Security Topics -- Recommend authorization code instead of implicit
>  
> Hi Nat, 
> 
>> Am 28.11.2018 um 21:10 schrieb n-sakimura <[e-mail]>:
>> 
>> I would support
>> 
>> 1) clearly defining Implicit as the flow that returns access token from the authorization endpoint ( some people confuses implicit as the flow that returns ID Token in the front channel)
> 
> That’s the current text: 
> 
> In order to avoid these issues, Clients SHOULD NOT use the implicit
>    grant or any other response type causing the authorization server to
>    issue an access token in the authorization response.
> 
> What would you like to modify? 
> 
>> 
>> 2) Banning the returning of the access token that are not sender constrained from the authorization endpoint
> 
> In order to avoid these issues, Clients SHOULD NOT use the implicit
>    grant or any other response type causing the authorization server to
>    issue an access token in the authorization response, if this access tokens is not sender-constraint.
> 
> What about this?
> 
> kind regards,
> Torsten.
> 
>> 
>> Best,
>> 
>> Nat
>> 
>> 
>> Outlook for iOS を入手
>>  
>> 差出人: OAuth <[e-mail]> (Dick Hardt <[e-mail]> の代理)
>> 送信日時: 水曜日, 11月 28, 2018 8:58 午後
>> 宛先: Hannes Tschofenig
>> Cc: [e-mail]
>> 件名: Re: [OAUTH-WG] OAuth Security Topics -- Recommend authorization code instead of implicit
>>  
>> +1
>> 
>> While there are various mechanisms to alleviate some of the issues of implicit, I don't think we can recommend specifics, and there may be future ones in the future. I think we all agree that implicit without any mitigation is problematic. 
>> 
>> How about we recommend against using implicit alone? 
>> 
>> 
>> On Mon, Nov 19, 2018 at 2:34 AM Hannes Tschofenig <[e-mail]> wrote:
>> Hi all,
>> 
>> The authors of the OAuth Security Topics draft came to the conclusion that it is not possible to adequately secure the implicit flow against token injection since potential solutions like token binding or JARM are in an early stage of adoption. For this reason, and since CORS allows browser-based apps to send requests to the token endpoint, Torsten suggested to use the authorization code instead of the implicit grant in call cases in his presentation (see https://datatracker.ietf.org/meeting/103/materials/slides-103-oauth-sessb-draft-ietf-oauth-security-topics-01).
>> 
>> A hum in the room at IETF#103 concluded strong support for his recommendations. We would like to confirm the discussion on the list.
>> 
>> Please provide a response by December 3rd.
>> 
>> Ciao
>> 
>> Hannes & Rifaat
>> 
>>  
>> 
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