Re: [OAUTH-WG] Implementation questions around refresh token rotation

Torsten Lodderstedt <torsten@lodderstedt.net> Sat, 10 October 2020 10:10 UTC

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From: Torsten Lodderstedt <torsten@lodderstedt.net>
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Date: Sat, 10 Oct 2020 12:10:13 +0200
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Cc: Aaron Parecki <aaron@parecki.com>, OAuth WG <oauth@ietf.org>
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To: Neil Madden <neil.madden@forgerock.com>
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Subject: Re: [OAUTH-WG] Implementation questions around refresh token rotation
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> Am 07.10.2020 um 09:20 schrieb Neil Madden <neil.madden@forgerock.com>om>:
> 
> 
> 
>>> On 6 Oct 2020, at 23:05, Aaron Parecki <aaron@parecki.com> wrote:
>>> 
>> 
>> Hi all, I have a couple questions for those of you who have implemented refresh token rotation...
>> 
>> Have you included the option of a grace period on refresh token use, allowing multiple uses within some time window? I'm wondering because a grace period where a refresh token may be used more than once would work around the problem that has been brought up, of a mobile app accidentally using a refresh token more than once during normal operation because different threads are unable to coordinate between themselves. However that also kind of defeats the purpose since attacks within that grace period would be hard to detect. I'm looking for an idea of where people have landed on that issue in practice.
> 
> Right. We’ve avoided adding a grace period for this reason. An attacker in a position to steal a refresh token is also presumably in a position to see when the legitimate client uses it and then sneak in just afterwards within the grace period. You could maybe only allow grace period refreshes from the same IP address but I’m not sure that would always hold in the flaky mobile network scenarios (eg refresh fails on 2G due to disconnect then client switches to Wifi hotspot and retries). 

We did not implement a grace period for the same reason. Refresh token rotation is a countermeasure against refresh token theft and replay for public client. A grace period to some degree limits it effectiveness against exactly this attack.

best regards,
Torsten.

> 
>> If you have implemented a grace period, then how do you handle expiring the additional refresh tokens that have been granted? For example, if RT "R1" is used twice, resulting in new ATs "A1.1", "A1.2" and new RTs "R1.1" and "R1.2", what happens if "R1.2" is then later used? Would you invalidate "R1.1" at that point? If so, why, and if not, why not?
>> 
>> It would be most interesting to hear practical experience from people who have already built refresh token rotation into a system.
>> 
>> Thanks!
>> 
>> ---
>> Aaron Parecki
>> https://aaronparecki.com
>> 
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