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 <da...@quizlet.com>
To: oauth@ietf.org
Cc: Quizlet Dev Team <devt...@quizlet.com>
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
Regards,
Dave
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