Re: [OAUTH-WG] Second WGLC on "JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens"

Vladimir Dzhuvinov <> Sun, 19 April 2020 08:50 UTC

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From: Vladimir Dzhuvinov <>
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Subject: Re: [OAUTH-WG] Second WGLC on "JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens"
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On 16/04/2020 10:10, Dominick Baier wrote:
> *iat vs nbf*
> What’s the rationale for using iat instead of nbf. Aren’t most JWT
> libraries (including e.g. the .NET one) looking for nbf by default?

Developers often tend to intuitively pick up "iat" over "nbf" because it
sounds more meaningful (my private observation). So given the empirical
approach of Vittorio to the spec, I suspect that's how "iat" got here.

If we bother to carefully look at the JWT spec we'll see that "iat" is
meant to be "informational" whereas it's "nbf" that is intended to serve
(together with "exp") in determining the actual validity window of the JWT.

My suggestion is to require either "iat" or "nbf". That shouldn't break
anything, and deployments that rely on one or the other to determine the
validity window of the access token can continue using their preferred
claim for that.