Oh, I see what you mean... however as Justin clarified, the discussion
here is not about GET vs POST, but rather about user agent vs client
making the request. The former distinction doesn't really matter in this
case, whereas in the latter distinction the client option seems to be
breaking the spec (only the user agent should send it).
Amichai
On 5/26/21 4:15 AM, Sascha Preibisch wrote:
Amichai,
I know POST won't be seen often, but the /authorize endpoint may still
accept POST as described here:
https://tools.ietf.org/html/rfc6749#section-3.1
<https://tools.ietf.org/html/rfc6749#section-3.1>
I hope this helps,
Sascha
On Tue., May 25, 2021, 13:00 A. Rothman, <amich...@amichais.net
<mailto:amich...@amichais.net>> wrote:
Hi Sacha,
Thanks for the links and video!
However I don't think this is what they're doing. There's no par
endpoint, no JSON response (just a redirect with a Location
header, that instead of following, the client is supposed to pass
through to the user agent), etc. It seems more like a regular
OAUTH2 flow, just with the initial request coming out of the
client instead of the user agent, without any of the specifics of
the par mentioned in the video.
btw, where does RFC 6749 say the authorization request can be sent
by the client? In the quote I made below from 4.1, as well as e.g.
4.2.1, it seems pretty explicit that it's the user agent that
makes the actual HTTP request (Authorization Request with all its
params etc), after being redirected to it from the client, no? I
don't see much wiggle room there to allow for the client to be
sending it itself...
Amichai
On 5/25/21 6:28 PM, Sascha Preibisch wrote:
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
<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
<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 <amich...@amichais.net
<mailto:amich...@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
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