Return-Path: 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 C5E4621F8B6F for ; Fri, 16 Sep 2011 11:59:00 -0700 (PDT) X-Virus-Scanned: amavisd-new at amsl.com X-Spam-Flag: NO X-Spam-Score: -2.149 X-Spam-Level: X-Spam-Status: No, score=-2.149 tagged_above=-999 required=5 tests=[AWL=0.100, BAYES_00=-2.599, HELO_EQ_DE=0.35, HTML_MESSAGE=0.001] Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ZOALJCduuad4 for ; Fri, 16 Sep 2011 11:58:58 -0700 (PDT) Received: from smtprelay05.ispgateway.de (smtprelay05.ispgateway.de [80.67.31.97]) by ietfa.amsl.com (Postfix) with ESMTP id 0705321F8B5B for ; Fri, 16 Sep 2011 11:58:57 -0700 (PDT) Received: from [87.142.251.121] (helo=[192.168.71.26]) by smtprelay05.ispgateway.de with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.68) (envelope-from ) id 1R4dex-00021w-3x; Fri, 16 Sep 2011 21:01:11 +0200 Message-ID: <4E739D06.2020309@lodderstedt.net> Date: Fri, 16 Sep 2011 21:01:26 +0200 From: Torsten Lodderstedt User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:6.0.2) Gecko/20110902 Thunderbird/6.0.2 MIME-Version: 1.0 To: Dave Rochwerger References: <1315434454.76681.YahooMailNeo@web31816.mail.mud.yahoo.com><0F38FE37-5F91-48ED-AD9E-1F08B7AA8DA6@oracle.com> <59CDCC16-44BA-4626-B744-F1169A13A542@oracle.com> <55876c26dbad646336c557dc22d67c40@lodderstedt-online.de> <4E7105DD.7030507@lodderstedt.net> In-Reply-To: Content-Type: multipart/alternative; boundary="------------080907050807020602040607" X-Df-Sender: dG9yc3RlbkBsb2RkZXJzdGVkdC1vbmxpbmUuZGU= Cc: oauth@ietf.org Subject: Re: [OAUTH-WG] OAuth2 Implementation questions (client secret andrefresh tokens) X-BeenThere: oauth@ietf.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: OAUTH WG List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Sep 2011 18:59:00 -0000 This is a multi-part message in MIME format. --------------080907050807020602040607 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Hi Dave, there has been a long debate about native client security and you can also find a comprehensive analysis in the security document. It's just a fact that such clients cannot reliably be authenticated in a public environment (even if malicious clients can be detected in some cases). So it is the responsibility of the resource owner to validate the authenticity/trustworthiness of an app before using it. The authz server's task is to authz access to cloud resources, so it asks the resource owner for consent. Once the consent is given, the refresh token itself represents the fact that the holder should be a legitimate client. regards, Torsten. ------------------------------------------------------------------------ *From: * Dave Rochwerger *Date: *Wed, 14 Sep 2011 13:45:42 -0700 *To: *Torsten Lodderstedt *Cc: * *Subject: *Re: [OAUTH-WG] OAuth2 Implementation questions (client secret and refresh tokens) Is this a security issue in the OAuth2 process then (for mobile apps using the authorization code flow)? 1. The draft says that mobile apps should be considered public clients because mobile apps can be decompiled and can not keep their credentials private. 2. In this case then, the draft says for these mobile apps to not authenticate with the secret and instead for the server to verify the redirect URI (and make it mandatory). 3. You said that verifying the redirect URI is not good enough to verify the client's identity. What am I missing? Thanks, Dave On Wed, Sep 14, 2011 at 12:51 PM, Torsten Lodderstedt > wrote: Hi Dave, redirect URI validation does not authenticate a client. For example, a URI registered for a private web client could be used by a (malicious) native app to assume the web app's identity. The client secret, in contrast, can be used to authenticate it. regards, Torsten. Am 14.09.2011 19:12, schrieb Dave Rochwerger: Thanks for the follow up, Torsten. Whilst I have your attention - any thoughts on my second question, about the use of a client secret? If for all clients we mandated registered URIs and verified them (whether they are private and public), what additional security does the client secret actually provide for private clients in the authorization code flow? Thanks, Dave On Wed, Sep 14, 2011 at 7:20 AM, Torsten Lodderstedt > wrote: Hi Dave, On Wed, 7 Sep 2011 17:22:14 -0700, Dave Rochwerger wrote: 1. "The user does not have to be present." Maybe I should be more clear. What benefit does that have over just a long-lived (forever) access token? The cost is the extra complication for 3rd party developers to have to worry about refresh tokens. I can not see a benefit in our model (everything over SSL, etc) to use refresh tokens. I want to use refresh tokens - but only if there is a reason for them, which I can not see at the moment. The benefit of refresh tokens significantly depends on your access token design. If your access tokens are just a pointer to a database you lookup on any API call, the only benefit if token rotation (coming back to this topic below). But your access tokens could also directly contain all user data you need to actually authorize API access. That way you could save DB lookups, which scales much better. In this model, revocation is much can be easier implement using refresh tokens. I think this is what Eran refered to. 2. "As Eran points out, you'd have to have do a DB lookup to have true revocation." The act of revoking tokens is not a common occurrence, DB lookups to revoke tokens is not a concern as there is more time spent by the user navigating the UI (or network latency, etc) than the cost of the DB call. 3. "In this sense you get the best of a long-lived credential, combined with good key rotation and authorization re-verification without having to re-involve the end-user." That all sounds good, but in our situation (all SSL, etc) - what do we want key rotation and re-verification for? I fail to see a reasonable vector for access token leakage to warrant any of this in our case. rotation is a mean to detect tokem theft from the device (see also http://tools.ietf.org/html/draft-lodderstedt-oauth-security-01#section-4.1.2). regards, Torsten. On Wed, Sep 7, 2011 at 5:08 PM, Phil Hunt wrote: See below... Phil @independentid www.independentid.com [11] phil.hunt@oracle.com [12] On 2011-09-07, at 4:57 PM, Dave Rochwerger wrote: Hi Phil,>> The client is then forced to periodically reauthenticate (without the user) before getting a new access token. What benefit does that have? The user does not have to be present. Refresh also gives the authzn server a chance to revoke access. Hence it is better to use shorter lived access tokens with long lived refresh tokens. That doesn't follow - we can just as easily revoke the single long-lived access token. As Eran points out, you'd have to have do a DB lookup to have true revocation. But, by having a short expiration time on the access token (say 1 hour or less), you get quasi-revocation which has to be re-validated after the access token expires and the client has to re-authenticate and provide a valid refresh token. In this sense you get the best of a long-lived credential, combined with good key rotation and authorization re-verification without having to re-involve the end-user. Dave.> On Wed, Sep 7, 2011 at 4:24 PM, Phillip Hunt wrote: You can also use a long lived refresh token in combination with a short access token. The client is then forced to periodically reauthenticate (without the user) before getting a new access token. Refresh also gives the authzn server a chance to revoke access. Hence it is better to use shorter lived access tokens with long lived refresh tokens. Phil On 2011-09-07, at 15:27, William Mills wrote: I'll talk to the refresh token question: they give you a hook for extensibility and key rotation. If you want to rotate your encryption keys or extend the data carried in the token in any way then you want to be able to cleanly refresh your tokens. Note that the refresh flow allows you to issue a new refresh token at the same time. It also allows a clean path to convert tokens in a new client if you decide you want SAML tokens instead of MAC for example. If you want those things you want to use refresh tokens. You can have long lived access tokens too, and just use the refresh tokens when you want to do something new with the access tokens. -bill ------------------------- FROM: Dave Rochwerger TO: oauth@ietf.org [2] CC: Quizlet Dev Team SENT: Wednesday, September 7, 2011 2:15 PM SUBJECT: [OAUTH-WG] OAuth2 Implementation questions (client secret and refresh tokens) Hi all, I have been implementing OAuth2 based on the various drafts for our new API. Initially, I implemented everything as per the spec, but due to our particular scenario and restrictions we have in place, there are some fundamental questions that I am unable to defend. I am hoping this group could help answer them for me. Our scenario: ========== * We are implementing an API to allow 3rd party developers to access users' protected resources via their applications. The applications will mostly be native phone apps, but some will have web server backends (javascript-only applications are not a concern at the moment). * We want to provide very long-lived (forever) tokens. * We are implementing the "authorization code" flow as that seems best suited to us (we don't want the implicit flow because end-users would have to re-authorize every hour). Our architecture: ============ * We control both the API server and the authorization server. * All requests to protected resources (ie: to the API server) are always done over SSL. * All requests to the authz server (token and authorize endpoints) are always done over SSL. * We enforce that every client must supply the state parameter (and our guidelines say they must verify the state for CSRF mitigation). * We enforce that every client must register a redirect URI. * We validate the redirect_uri used to request an access token is the same that was used to obtain the auth code. * The only time a request is not made over SSL is the redirect with the auth_code which is very short-lived (30 seconds) and is tied to a verified redirect URI. * We enforce that access tokens must be provided using the Authorization header only (and of course, over SSL). * We have guidelines saying that all mobile apps must use the native browser (and not an embedded web UI). Questions: ======== 1. Given the above scenario, what use are refresh tokens? - Access tokens can not leak because every request (to resource and authz server) containing an access token is done over SSL. We control both the authz and resource servers, so tokens in logs (and other suggested reasons in the archives) are not an issue. - Long-lived refresh tokens and short-lived access tokens are supposed to provide security due to possible access token leakage... but in our 100% SSL scenario, if access tokens are able to leak, then so would the client id, secret and refresh token. - Having a long-lived refresh token that can be exchanged for another access token adds a level of complexity (a second HTTPS request every so often) and seems to provide no benefit for our case. 2. What is the point of the client secret (in our scenario)? - We originally were treating the clients as confidential, but after re-reading the native-application section, it seems we really should treat them as public (phone apps can be decompiled and the secret discovered). - The spec says that the authz server should authenticate confidential clients, but public clients are allowed to just send their public client id (and no secret). - The only verification then, is to enforce redirect URI registration and to validate the redirect URI between authorization and token steps. So, the question is, assuming that we, one: "enforce redirect-URI registration" and two: "validate that URI" - why can't we treat all clients as public and not worry about a secret? What is the benefit of having confidential clients (and a secret) at all? Our API source is not available, but the oauth2 server implementation can be seen here: https://github.com/quizlet/oauth2-php [4] Regards, Dave _______________________________________________ OAuth mailing list OAuth@ietf.org [5] https://www.ietf.org/mailman/listinfo/oauth [6] _______________________________________________ OAuth mailing list OAuth@ietf.org [7] https://www.ietf.org/mailman/listinfo/oauth [8] Links: ------ [1] mailto:daver@quizlet.com [2] mailto:oauth@ietf.org [3] mailto:devteam@quizlet.com [4] https://github.com/quizlet/oauth2-php [5] mailto:OAuth@ietf.org [6] https://www.ietf.org/mailman/listinfo/oauth [7] mailto:OAuth@ietf.org [8] https://www.ietf.org/mailman/listinfo/oauth [9] mailto:wmills@yahoo-inc.com [10] mailto:phil.hunt@oracle.com [11] http://www.independentid.com [12] mailto:phil.hunt@oracle.com [13] mailto:phil.hunt@oracle.com _______________________________________________ OAuth mailing list OAuth@ietf.org https://www.ietf.org/mailman/listinfo/oauth --------------080907050807020602040607 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: 8bit Hi Dave,

there has been a long debate about native client security and you can also find a comprehensive analysis in the security document.

It's just a fact that such clients cannot reliably be authenticated in a public environment (even if malicious clients can be detected in some cases). So it is the responsibility of the resource owner to validate the authenticity/trustworthiness of an app before using it. The authz server's task is to authz access to cloud resources, so it asks the resource owner for consent. Once the consent is given, the refresh token itself represents the fact that the holder should be a legitimate client.

regards,
Torsten.
From: Dave Rochwerger <daver@quizlet.com>
Date: Wed, 14 Sep 2011 13:45:42 -0700
To: Torsten Lodderstedt<torsten@lodderstedt.net>
Subject: Re: [OAUTH-WG] OAuth2 Implementation questions (client secret and refresh tokens)

Is this a security issue in the OAuth2 process then (for mobile apps using the authorization code flow)?

1. The draft says that mobile apps should be considered public clients because mobile apps can be decompiled and can not keep their credentials private.
2. In this case then, the draft says for these mobile apps to not authenticate with the secret and instead for the server to verify the redirect URI (and make it mandatory).
3. You said that verifying the redirect URI is not good enough to verify the client's identity.

What am I missing?

Thanks,
Dave


On Wed, Sep 14, 2011 at 12:51 PM, Torsten Lodderstedt <torsten@lodderstedt.net> wrote:
Hi Dave,

redirect URI validation does not authenticate a client. For example, a URI registered for a private web client could be used by a (malicious) native app to assume the web app's identity. The client secret, in contrast, can be used to authenticate it.

regards,
Torsten.

Am 14.09.2011 19:12, schrieb Dave Rochwerger:

Thanks for the follow up, Torsten.

Whilst I have your attention - any thoughts on my second question,
about the use of a client secret?
If for all clients we mandated registered URIs and verified them
(whether they are private and public), what additional security does
the client secret actually provide for private clients in the
authorization code flow?


Thanks,
Dave

On Wed, Sep 14, 2011 at 7:20 AM, Torsten Lodderstedt
<torsten@lodderstedt.net>  wrote:
Hi Dave,


On Wed, 7 Sep 2011 17:22:14 -0700, Dave Rochwerger wrote:

1. "The user does not have to be present."
Maybe I should be more clear. What benefit does that have over just a
long-lived (forever) access token? The cost is the extra complication for
3rd party developers to have to worry about refresh tokens. I can not see
a benefit in our model (everything over SSL, etc) to use refresh tokens.
I want to use refresh tokens - but only if there is a reason for them,
which I can not see at the moment.

The benefit of refresh tokens significantly depends on your access token design. If your access tokens are just a pointer to a database you lookup on any API call, the only benefit if token rotation (coming back to this topic below). But your access tokens could also directly contain all user data you need to actually authorize API access. That way you could save DB lookups, which scales much better. In this model, revocation is much can be easier implement using refresh tokens. I think this is what Eran refered to.


2. "As Eran points out, you'd have to have do a DB lookup to have true
revocation."
The act of revoking tokens is not a common occurrence, DB lookups to
revoke tokens is not a concern as there is more time spent by the user
navigating the UI (or network latency, etc) than the cost of the DB call.

3. "In this sense you get the best of a long-lived credential, combined
with good key rotation and authorization re-verification without having
to re-involve the end-user."
That all sounds good, but in our situation (all SSL, etc) - what do we
want key rotation and re-verification for? I fail to see a reasonable
vector for access token leakage to warrant any of this in our case.

rotation is a mean to detect tokem theft from the device (see also http://tools.ietf.org/html/draft-lodderstedt-oauth-security-01#section-4.1.2).

regards,
Torsten.

On Wed, Sep 7, 2011 at 5:08 PM, Phil Hunt wrote:

See below...

Phil
@independentid
www.independentid.com [11] phil.hunt@oracle.com [12]


On 2011-09-07, at 4:57 PM, Dave Rochwerger wrote:

Hi Phil,>>  The client is then forced to periodically reauthenticate
(without the user) before getting a new access token.
What benefit does that have?
The user does not have to be present.

Refresh also gives the authzn server a chance to revoke access.
Hence it is better to use shorter lived access tokens with long lived
refresh tokens.
That doesn't follow - we can just as easily revoke the single
long-lived access token.
As Eran points out, you'd have to have do a DB lookup to have true
revocation. But, by having a short expiration time on the access token
(say 1 hour or less), you get quasi-revocation which has to be
re-validated after the access token expires and the client has to
re-authenticate and provide a valid refresh token. In this sense you
get the best of a long-lived credential, combined with good key
rotation and authorization re-verification without having to re-involve
the end-user.

Dave.>
On Wed, Sep 7, 2011 at 4:24 PM, Phillip Hunt wrote:

You can also use a long lived refresh token in combination with a
short access token. The client is then forced to periodically
reauthenticate (without the user) before getting a new access
token.
Refresh also gives the authzn server a chance to revoke access.
Hence it is better to use shorter lived access tokens with long
lived refresh tokens.

Phil

On 2011-09-07, at 15:27, William Mills wrote:

I'll talk to the refresh token question: they give you a hook for
extensibility and key rotation. If you want to rotate your
encryption keys or extend the data carried in the token in any
way then you want to be able to cleanly refresh your tokens. Note
that the refresh flow allows you to issue a new refresh token at
the same time. It also allows a clean path to convert tokens in a
new client if you decide you want SAML tokens instead of MAC for
example.
If you want those things you want to use refresh tokens. You can
have long lived access tokens too, and just use the refresh
tokens when you want to do something new with the access tokens.
-bill

-------------------------
FROM: Dave Rochwerger
TO: oauth@ietf.org [2]
CC: Quizlet Dev Team
SENT: Wednesday, September 7, 2011 2:15 PM
SUBJECT: [OAUTH-WG] OAuth2 Implementation questions (client

secret and refresh tokens)

Hi all,
I have been implementing OAuth2 based on the various drafts for
our new API. Initially, I implemented everything as per the spec,
but due to our particular scenario and restrictions we have in
place, there are some fundamental questions that I am unable to
defend.
I am hoping this group could help answer them for me.
Our scenario:
==========
* We are implementing an API to allow 3rd party developers to
access users' protected resources via their applications. The
applications will mostly be native phone apps, but some will have
web server backends (javascript-only applications are not a
concern at the moment).
* We want to provide very long-lived (forever) tokens.
* We are implementing the "authorization code" flow as that seems
best suited to us (we don't want the implicit flow because
end-users would have to re-authorize every hour).
Our architecture:
============
* We control both the API server and the authorization server.
* All requests to protected resources (ie: to the API server) are
always done over SSL.
* All requests to the authz server (token and authorize
endpoints) are always done over SSL.
* We enforce that every client must supply the state parameter
(and our guidelines say they must verify the state for CSRF
mitigation).
* We enforce that every client must register a redirect URI.
* We validate the redirect_uri used to request an access token is
the same that was used to obtain the auth code.
* The only time a request is not made over SSL is the redirect
with the auth_code which is very short-lived (30 seconds) and is
tied to a verified redirect URI.
* We enforce that access tokens must be provided using the
Authorization header only (and of course, over SSL).
* We have guidelines saying that all mobile apps must use the
native browser (and not an embedded web UI).
Questions:
========
1. Given the above scenario, what use are refresh tokens?
- Access tokens can not leak because every request (to resource
and authz server) containing an access token is done over SSL. We
control both the authz and resource servers, so tokens in logs
(and other suggested reasons in the archives) are not an issue.
- Long-lived refresh tokens and short-lived access tokens are
supposed to provide security due to possible access token
leakage... but in our 100% SSL scenario, if access tokens are
able to leak, then so would the client id, secret and refresh
token.
- Having a long-lived refresh token that can be exchanged for
another access token adds a level of complexity (a second HTTPS
request every so often) and seems to provide no benefit for our
case.
2. What is the point of the client secret (in our scenario)? -
We originally were treating the clients as confidential, but
after re-reading the native-application section, it seems we
really should treat them as public (phone apps can be decompiled
and the secret discovered).

- The spec says that the authz server should authenticate
confidential clients, but public clients are allowed to just send
their public client id (and no secret).
- The only verification then, is to enforce redirect URI
registration and to validate the redirect URI between
authorization and token steps.

So, the question is, assuming that we, one: "enforce
redirect-URI registration" and two: "validate that URI" - why
can't we treat all clients as public and not worry about a
secret?
What is the benefit of having confidential clients (and a secret)
at all?
Our API source is not available, but the oauth2 server
implementation can be seen here:
https://github.com/quizlet/oauth2-php [4]

Regards,
Dave

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OAuth mailing list
OAuth@ietf.org [5]
https://www.ietf.org/mailman/listinfo/oauth [6]

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OAuth mailing list
OAuth@ietf.org [7]
https://www.ietf.org/mailman/listinfo/oauth [8]



Links:
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[1] mailto:daver@quizlet.com
[2] mailto:oauth@ietf.org
[3] mailto:devteam@quizlet.com
[4] https://github.com/quizlet/oauth2-php
[5] mailto:OAuth@ietf.org
[6] https://www.ietf.org/mailman/listinfo/oauth
[7] mailto:OAuth@ietf.org
[8] https://www.ietf.org/mailman/listinfo/oauth
[9] mailto:wmills@yahoo-inc.com
[10] mailto:phil.hunt@oracle.com
[11] http://www.independentid.com
[12] mailto:phil.hunt@oracle.com
[13] mailto:phil.hunt@oracle.com

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