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

[Dave Tonge <[e-mail]>]

> Our goal is to prevent cases where we lose the ability to Refresh a Token
due to transient issues (which have run the gamut from network problems to
bad software updates on the AS side).

We've seen this issue quite a bit and it's very frustrating. I would
suggest that refresh token rotation is not used for confidential clients
that authenticate with private_key_jwt or tls_client_auth.

On Wed, 7 Oct 2020 at 00:57, Jeff Craig <jeffcraig=
[e-mail]> wrote:

> My experience is more from the Client side of the equation on this
> problem, but I do have some thoughts. Our goal is to prevent cases where we
> lose the ability to Refresh a Token due to transient issues (which have run
> the gamut from network problems to bad software updates on the AS side).
> Our use case also does all token handling server-side, so our threat model
> is not the same as the mobile application you described. There is a clear
> tradeoff in reducing user friction with additional authorization events,
> and securing access.
>
> The recommendation my team typically gives people building Authorization
> Servers with Refresh Token Rotation is to keep the old refresh token until
> they see the new one (which means that there are generally two refresh
> tokens valid at any point in time, an unfortunate trade-off). A more
> difficult, but potentially plausible implementation would be to hold onto
> the older Refresh Token until the newly issued Access Token is used (thus
> implying the refresh was successful on both sides).
>
> We aren't trying to protect against multiple in-flight refreshes though
> (we've done a LOT of work to attempt to remove that possibility in a
> globally consistent manner), we're trying to protect against a network
> interruption that prevents the first use of R1, so our assumption is that
> R2.1 was completely lost, and only R2.2 matters moving forward. Meaning: R1
> is sent, A/R2.1 is dropped in flight, R1 is sent again, A/R2.2 is returned
> and stored. Since R1 was seen a second time, we recommend that R2.1 be
> ignored in future. Next refresh will use R2.2, at which point R1 should
> never be seen again.
>
> The biggest issue that I see with a time-based grace period is that for
> many offline tasks, a single refresh failure may be ignored by the client,
> and it could be hours before the second refresh attempt using the older
> refresh token is made (depending on time of day and what these requests are
> being used for), making the grace period low value in that case.
>
> On Tue, Oct 6, 2020 at 5:28 PM <vittorio.bertocci=
> [e-mail]> wrote:
>
>> Hey Aaron,
>>
>> Auth0 does offer a configurable grace period, during which the
>> “preceding” token can be reused.
>>
>> I am not 100% sure what we do in the exact scenario you described, and I
>> will double check for you, but here’s my intuition.
>>
>>
>>
>> The operation redeem(RT_n) should result in AT, RT_n+1. The grace period
>> just extends the time in which the operation can occur, but every operation
>> should be idempotent. All repeats of that operation within the grace period
>> should have the same result, which means that every resulting RT is a
>> representative of the RT_n+1 class, hence all valid at the same time. After
>> the grace period elapses, RT_n is invalid, and that’s it.
>>
>> So, in your example I would consider RT1.1 and RT1.2 as equivalent, as
>> they are both representatives of the RT_n+1 equivalence class.
>>
>>
>>
>> It would be very hard to do otherwise, given that network operations
>> aren’t guaranteed to be concluded in the order they were executed without
>> semaphores, and above all the network failures the grace period is designed
>> to handle can apply to any of the requests, regardless of the order.
>>
>>
>>
>> *From:* OAuth <[e-mail]> *On Behalf Of *Aaron Parecki
>> *Sent:* Tuesday, October 6, 2020 3:06 PM
>> *To:* OAuth WG <[e-mail]>
>> *Subject:* [OAUTH-WG] Implementation questions around refresh token
>> rotation
>>
>>
>>
>> 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.
>>
>>
>>
>> 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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-- 
Dave Tonge

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