Re: [OAUTH-WG] expires_in

This is probably a best practice, but we should be careful to not oversell the benefits. Unless you measure token lifetime in a small number of seconds, then it’s doubtful that any realistic attack will be stopped by this. It’s mostly useful at defending against opportunistic attacks - e.g. a token accidentally gets logged, but the logs aren’t examined very often. Sender-constrained/PoP tokens, avoiding passing tokens in URL parameters, and so on are better defences against this kind of thing.

There are two deployment scenarios when short-lived access token are essential though:

1. If you are employing the “self-contained RS” model (no introspection calls to the AS) and are using short-lived access tokens with a refresh token to force the client to check in with the AS periodically to allow token revocation. [1]

2. If you are using a blacklisting strategy to token revocation, in which case having a short token lifetime limits the amount of time you need to blacklist tokens for.

On the other hand, is there ever a valid reason for having an access token be valid for 10 years or so?

[1] https://www.ietf.org/mail-archive/web/oauth/current/msg06687.html

— Neil

> On 18 Dec 2018, at 08:55, Hannes Tschofenig <Hannes.Tschofenig@arm.com> wrote:
> 
> Hi all,
> 
> In a recent email conversation on the IETF ACE mailing list Ludwig Seitz suggested that the expires_in claim in an access token should actually be mandatory.
> Intuitively it feels like access tokens shouldn't have an unrestricted lifetime. I am curious whether recommendations would be useful here.
> 
> RFC 6819 talks about the expires_in claim and says:
> 
> 3.1.2.  Limited Access Token Lifetime
> 
>   The protocol parameter "expires_in" allows an authorization server
>   (based on its policies or on behalf of the end user) to limit the
>   lifetime of an access token and to pass this information to the
>   client.  This mechanism can be used to issue short-lived tokens to
>   OAuth clients that the authorization server deems less secure, or
>   where sending tokens over non-secure channels.
> 
> draft-ietf-oauth-security-topics-10 only talks about refresh token expiry.
> 
> In OpenID Connect the expires_in claim is also optional.
> 
> Ciao
> Hannes
> 
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