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

[Aaron Parecki <[e-mail]>]

+1

I would also like to ensure there is a clear definition of "sender
constrained" tokens in this BCP.

Aaron


On Thu, Nov 29, 2018 at 10:06 AM Torsten Lodderstedt <
[e-mail]> wrote:

> Hi all,
>
> based on your feedback on the list and off list, Daniel and I polished the
> text. That’s our proposal:
>
> —
> In order to avoid these issues, clients MUST NOT use the implicit
> grant (response type "token") or any other response type issuing access
> tokens in the authorization response, such as "token id_token" and "code
> token id_token“,
> unless the issued access tokens are sender-constrained and access token
> injection in
> the authorization response is prevented.
> —
>
> Explantation:
> - we wanted to have the right balance between a generic definition of the
> response types we do not recommend/allow to be used and a
> concrete/actionable list of the affected response types.
> - we changed from SHOULD NOT to MUST NOT as suggested by Nat and supported
> by William
>
> We look forward to seeing your feedback.
>
> kind regards,
> Torsten.
>
> > Am 29.11.2018 um 15:15 schrieb John Bradley <[e-mail]>:
> >
> > I am ok with that.
> >
> > On Wed, Nov 28, 2018, 8:03 PM Torsten Lodderstedt <
> [e-mail] wrote:
> >
> > > 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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Aaron Parecki
aaronparecki.com
@aaronpk <http://twitter.com/aaronpk>