Re: [OAUTH-WG] Can a client send the Authorization Request?

Sascha Preibisch <saschapreibisch@gmail.com> Tue, 25 May 2021 15:29 UTC

Return-Path: <saschapreibisch@gmail.com>
X-Original-To: oauth@ietfa.amsl.com
Delivered-To: oauth@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 232F73A1078 for <oauth@ietfa.amsl.com>; Tue, 25 May 2021 08:29:14 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.097
X-Spam-Level:
X-Spam-Status: No, score=-2.097 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id SAKffzfrdDoY for <oauth@ietfa.amsl.com>; Tue, 25 May 2021 08:29:09 -0700 (PDT)
Received: from mail-lj1-x231.google.com (mail-lj1-x231.google.com [IPv6:2a00:1450:4864:20::231]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 7F20B3A1071 for <oauth@ietf.org>; Tue, 25 May 2021 08:29:09 -0700 (PDT)
Received: by mail-lj1-x231.google.com with SMTP id o8so38748192ljp.0 for <oauth@ietf.org>; Tue, 25 May 2021 08:29:09 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=pCUhJi0ItK71FzqNW2ehdUIp513AFkasLbBsaqvFKvE=; b=uDoXO0U6gsWWGkcHPqrI5jVbxaMqcAWOQcJvl++QwaSPzYTF3g92NtW+hCeghpt3ya x/LDZWDOT55kI+TZPQTI0MTFkE0M4WVWS8YpNdHKrt8xi+cRiAebkMOEwmjz8PLzmlbm SqIVAforL4mOX9frihfh0qlxjDvWWLbatZAAfi4p6c573J/JpYSPGIuymqOjyushxb3b ThMfsqA5KE1HTsi21RNNTFSaBjNceHfQcwblThqvROaQzSucD2jDZP7yWaEPgLVa5tIn TTBhQHTe5cRYK4TaggbxnE/3CHsgswZKKSB7WwdFMIgN4xmoK9QsvJEeLGtyiBEErXZ9 K1vA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=pCUhJi0ItK71FzqNW2ehdUIp513AFkasLbBsaqvFKvE=; b=gRpq+tFaGwNZJBTcU3pjRxHn90lv/p1oCLzrPys9Es6+zhp7G/RBzEuGEvKTFzNjJS kOPYDrfeL7eMT9Cdl+cLOicd/1rM4gvs2soDLTWAxpR7VNy3uOL0t3Yj83lBsFr+Gw13 XfvDpm5214Plaf1ttZEKYIxsIgRdy3XzAMJ73kDbtqbTPoMoFf+8p0HyRufOMb9FycBs NOgRD0izQztnyEK2BPxJXgfIqE1jo/c9S9Rw4b/gMu8BkvqpcSFUMx045KIy6lEWuG87 O5GoINRrZWeEhRhPh/kNQ4birNuPOoBbP8+4lcR4Qk+mAZGaVSzhh2UC0Dfwdebkx5Wa DH8A==
X-Gm-Message-State: AOAM530bFRRDtGzUVpb9ioL4HP+w/IySa7n3JGJTApnFhWi8dz8njR9M COvJrtbyr+PdK4Wh1BwwaDv9oCfzv/mgh87WXtHWl+GrLlpVZw==
X-Google-Smtp-Source: ABdhPJy2zpAlOucLuD+BKz/AMsTOBAUF8AUz7M9h6folmikl8C9SMOwoyl9XVeVVm1I8xgLQwuPndonWLbZV1BtXSlY=
X-Received: by 2002:a05:651c:487:: with SMTP id s7mr22236058ljc.351.1621956547181; Tue, 25 May 2021 08:29:07 -0700 (PDT)
MIME-Version: 1.0
References: <952456782.01621954787444.JavaMail.root@shefa>
In-Reply-To: <952456782.01621954787444.JavaMail.root@shefa>
From: Sascha Preibisch <saschapreibisch@gmail.com>
Date: Tue, 25 May 2021 08:28:56 -0700
Message-ID: <CAP=vD9sq72MKuw37voGE-0FAHpDXS-QsaRDHK04d3jFuNunyHA@mail.gmail.com>
To: "A. Rothman" <amichai2@amichais.net>
Cc: IETF oauth WG <oauth@ietf.org>
Content-Type: multipart/alternative; boundary="000000000000d6027d05c3292f85"
Archived-At: <https://mailarchive.ietf.org/arch/msg/oauth/oihpzXeq7nYRkRhZwl3c3CK7oAI>
Subject: Re: [OAUTH-WG] Can a client send the Authorization Request?
X-BeenThere: oauth@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: OAUTH WG <oauth.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/oauth>, <mailto:oauth-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/oauth/>
List-Post: <mailto:oauth@ietf.org>
List-Help: <mailto:oauth-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/oauth>, <mailto:oauth-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 25 May 2021 15:29:14 -0000

Hello Amichai!

There could be several reasons why you see that behaviour in your web
browser. For example:

- This RFC suggests sending a request to the authorization server, get a
session specific URL back which can be forwarded to the authorization
server via the browser. This is OAuth PAR (Pushed Authorization Request):
https://datatracker.ietf.org/doc/html/draft-ietf-oauth-par. I have also
made a video about this flow, maybe it matches what you are seeing on your
web server: https://www.youtube.com/watch?v=fE11HJRCL-k

- In addition RFC 6749 also allows a client to POST to the authorization
endpoint

I hope this helps,
Sascha

On Tue, 25 May 2021 at 08:00, A. Rothman <amichai2@amichais.net> wrote:

> Hi,
>
> In RFC 6749 section 4.1, the Authorization Code Grant flow starts with:
>
> (A)  The client initiates the flow by directing the resource owner's
>          user-agent to the authorization endpoint.  The client includes
>          its client identifier, requested scope, local state, and a
>          redirection URI to which the authorization server will send the
>          user-agent back once access is granted (or denied).
>
> (B)  The authorization server authenticates the resource owner (via
>          the user-agent) and establishes whether the resource owner
>          grants or denies the client's access request.
>
>
>  From this, and most explanation I've seen, I understand that the client
> (e.g. my web server) is supposed to prepare the Authorization Request
> URL but instead of sending it to the Authorization Server, it redirects
> the user agent which is the one actually making the HTTP request. It
> then goes back and forth with the Authorization Server (with HTML and
> posting forms and whatnot), and eventually receives the Authorization
> Response which redirects the user agent back to the client's callback
> URL with the included code parameter. So as far as the Authorization
> Request/Response flow goes, there is no direct communications between
> the client and Authorization Server up to this point (before the token
> exchange).
>
> 1. Basically correct so far?
>
> Now, I've encountered a provider that works slightly differently (but
> still with the Authorization Code Grant scheme): the client (my web
> server) is supposed to send the Authorization Request directly to the
> Authorization Server, then receive some opaque URL, and redirect the
> user agent to there to continue the process. I suppose this URL is
> equivalent to one from the middle of the 'back and forth' in the
> previous scenario. The rest of the flow continues the same. So
> basically, the initial redirect response and HTTP request are reversed -
> instead of first redirect and then request (from user agent), there is
> first the request (from client)  and then redirect.
>
> So the questions are:
>
> 2. Is this compliant with the RFC?
>
> 3. Is it any less secure? (even if not strictly compliant with the RFC's
> flow, it may still be secure...)
>
> 4. If it is less secure, what are the possible vulnerabilities or
> attacks made possible here that are mitigated in the original flow?
>
> 5. They claim the change is made because they insist on using MTLS on
> all Authentication Server endpoints, including the Authorization
> Endpoint. Does this make sense? Does it add security, or is the OAUTH2
> flow just as secure without MTLS on the Authorization Endpoint?
>
> Thanks,
>
> Amichai
>
>
>
> _______________________________________________
> OAuth mailing list
> OAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/oauth
>