That's an interesting use-case for relay mode and might be a reason to cover it.

However, we believe the current code for the relay mode in draft-sakimura-oauth-wmrm-01 does not work. The same-origin policy should prevent this line from working:

messageTargetWindowReference = e.source.document.getElementById(web_message_target);

"e.source" references the main window (e.g., client.example.com). This means the (un)authenticated window (e.g., as.example.com) tries to access "document.getElementById" for the cross-origin main window. Due to the SOP the browser should throw a DOMException ("Failed to read a named property 'document' from 'Window': Blocked a frame with origin "https://as.example.com"; from accessing a cross-origin frame.")

As I said in the other response, we would be really interested in taking a look at existing implementations of draft-sakimura-oauth-wmrm-01 to see how they solve this problem.


Best regards,
Karsten


On 10.01.2024 10:15, Filip Skokan wrote:

    We do not consider the relay mode. The relay mode is motivated by
    the use of the implicit grant which is discouraged nowadays.


Motivation aside, if my memory serves right (and that's a big IF in this case), the relay mode was not limited to implicit responses and was useful regardless of the response type, e.g. in cases where the authorization request was triggered from an eTLD+1 top level window but the target was authenticating a service that ran on its subdomain, a landing page with a CTA to login sort of setup.

S pozdravem,
*Filip Skokan*


On Wed, 10 Jan 2024 at 09:47, Filip Skokan <panva...@gmail.com> wrote:

        our draft covers and is compatible to what's called "simple
        mode" (both with and without prompt) in
        draft-sakimura-oauth-wmrm-00/-01.


    So a client that's using a simple mode with web_message today
    could, without change, utilize your draft as well? That doesn't
    seem likely given the message structure is not the same as in
    draft-sakimura-oauth-wmrm. Is that an omission or intentional?

    S pozdravem,
    *Filip Skokan*


    On Wed, 10 Jan 2024 at 09:37, Karsten Meyer zu Selhausen |
    Hackmanit <karsten.meyerzuselhau...@hackmanit.de> wrote:

        Hello Filip,

        our draft covers and is compatible to what's called "simple
        mode" (both with and without prompt) in
        draft-sakimura-oauth-wmrm-00/-01.

        We do not consider the relay mode. The relay mode is motivated
        by the use of the implicit grant which is discouraged nowadays.

        The main differences to draft-sakimura-oauth-wmrm-01 can be
        summarized as follows:

          * In general we do not focus on "modes" but instead on the
            actual communication using the postMessage API. Our draft
            contains examples for the format/structure for the
            messages sent using the postMessage API.
          * Our draft enables iframe flows with user interaction while
            draft-sakimura-oauth-wmrm-01 only covers iframe flows
            without user interaction.
          * Our draft contains security considerations describing
            threats and giving recommendations to address them.
          * Our draft briefly discusses the implications of the 3rd
            party cookie phaseout for iframes.

        Our main motivation is the belief that there is a need for a
        specification defining how to securely use the postMessage API
        for OAuth auth. responses. The research of my co-authors
        underlines this need [1].

        As I said, at the last OSW there was agreement that it would
        be a good idea to write an RFC for a postMessage-based
        response mode. draft-sakimura-oauth-wmrm-00 was expired years
        ago and seemed to be inactive when we started to work on our
        own draft. In our opinion it is not a great option to rely on
        an expired draft. As for customers I work with this is not an
        option at all; they want to implement and use final RFCs
        whenever possible.

        We are looking for feedback from the WG and are open to
        collaborate with the authors of draft-sakimura-oauth-wmrm if
        they want to join the efforts.


        Best regards,
        Karsten

        [1] https://distinct-sso.com/

        On 04.01.2024 12:10, Filip Skokan wrote:
        Hello Karsten,

        Can you summarize in what ways is your draft compatible
        with draft-sakimura-oauth-wmrm-00? Which of the described
        modes in Nat's document does it cover?

        There are existing implementations (both partial and full)
        of draft-sakimura-oauth-wmrm-00 so if your draft is not
        compatible I would recommend not using the same response mode
        name/identifier in your proposal.

        What prompted you to start a new draft rather than
        using draft-sakimura-oauth-wmrm-00?

        S pozdravem,
        *Filip Skokan*


        On Thu, 4 Jan 2024 at 12:04, Karsten Meyer zu Selhausen |
        Hackmanit <karsten.meyerzuselhau...@hackmanit.de> wrote:

            Hi all,

            we would like to ask again for feedback on our draft for
            the "web_message" response mode:
            
*https://datatracker.ietf.org/doc/draft-meyerzuselha-oauth-web-message-response-mode/
            *

            We think it would be very helpful for implementers and
            developers to specify a secure standard for a postMessage
            API-based response mode.

            Best regards,
            Karsten*
            *

            On 23.11.2023 10:11, Karsten Meyer zu Selhausen |
            Hackmanit wrote:

            Hi everyone,

            at the last OSW the topic of a response mode based on
            the postMessage API came up. This approach is already
            used by multiple parties (e.g., Google) but lacks
            standardization.

            There was some sense of agreement that it would be a
            good idea to create an RFC defining this response mode
            to counter security flaws in individual implementations
            and improve interoperability.

            Because the efforts in the past were long expired (draft
            -00 of
            https://datatracker.ietf.org/doc/draft-sakimura-oauth-wmrm/
            expired in 2016) we took the initiative and started to
            work on a new ID for the "web_message" response mode.

            *We would like to to ask the members of the working
            group for feedback on our draft:
            
https://datatracker.ietf.org/doc/draft-meyerzuselha-oauth-web-message-response-mode/*


            I see that "draft-sakimura-oauth-wmrm" has been recently
            updated. However, there have not been any changes to its
            contents. What are the plans of the authors for this draft?

            Best regards
            Karsten

-- Karsten Meyer zu Selhausen
            Senior IT Security Consultant
            Phone:      +49 (0)234 / 54456499
            Web:        https://hackmanit.de  | IT Security Consulting, 
Penetration Testing, Security Training

            Multi-Factor Authentication (MFA) significantly increases the 
security of your accounts.
            Learn in our blog posts what the best MFA options are and how FIDO2 
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            Hackmanit GmbH
            Universitätsstraße 60 (Exzenterhaus)
            44789 Bochum

            Registergericht: Amtsgericht Bochum, HRB 14896
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Somorovsky, Dr. Christian Mainka, Prof. Dr. Marcus Niemietz

-- Karsten Meyer zu Selhausen
            Senior IT Security Consultant
            Phone:      +49 (0)234 / 54456499
            Web:        https://hackmanit.de  | IT Security Consulting, 
Penetration Testing, Security Training

            Multi-Factor Authentication (MFA) significantly increases the 
security of your accounts.
            Learn in our blog posts what the best MFA options are and how FIDO2 
goes one step further to solve the world’s password problem:
            https://www.hackmanit.de/en/blog-en/162-what-is-mfa
            https://www.hackmanit.de/en/blog-en/165-what-is-fido2

            Hackmanit GmbH
            Universitätsstraße 60 (Exzenterhaus)
            44789 Bochum

            Registergericht: Amtsgericht Bochum, HRB 14896
            Geschäftsführer: Prof. Dr. Jörg Schwenk, Prof. Dr. Juraj 
Somorovsky, Dr. Christian Mainka, Prof. Dr. Marcus Niemietz

            _______________________________________________
            OAuth mailing list
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-- Karsten Meyer zu Selhausen
        Senior IT Security Consultant
        Phone:  +49 (0)234 / 54456499
        Web:    https://hackmanit.de  | IT Security Consulting, Penetration 
Testing, Security Training

        Multi-Factor Authentication (MFA) significantly increases the security 
of your accounts.
        Learn in our blog posts what the best MFA options are and how FIDO2 
goes one step further to solve the world’s password problem:
        https://www.hackmanit.de/en/blog-en/162-what-is-mfa
        https://www.hackmanit.de/en/blog-en/165-what-is-fido2

        Hackmanit GmbH
        Universitätsstraße 60 (Exzenterhaus)
        44789 Bochum

        Registergericht: Amtsgericht Bochum, HRB 14896
        Geschäftsführer: Prof. Dr. Jörg Schwenk, Prof. Dr. Juraj Somorovsky, 
Dr. Christian Mainka, Prof. Dr. Marcus Niemietz

--
Karsten Meyer zu Selhausen
Senior IT Security Consultant
Phone:  +49 (0)234 / 54456499
Web:    https://hackmanit.de  | IT Security Consulting, Penetration Testing, 
Security Training

Multi-Factor Authentication (MFA) significantly increases the security of your 
accounts.
Learn in our blog posts what the best MFA options are and how FIDO2 goes one 
step further to solve the world’s password problem:
https://www.hackmanit.de/en/blog-en/162-what-is-mfa
https://www.hackmanit.de/en/blog-en/165-what-is-fido2

Hackmanit GmbH
Universitätsstraße 60 (Exzenterhaus)
44789 Bochum

Registergericht: Amtsgericht Bochum, HRB 14896
Geschäftsführer: Prof. Dr. Jörg Schwenk, Prof. Dr. Juraj Somorovsky, Dr. 
Christian Mainka, Prof. Dr. Marcus Niemietz

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