[jose] TTL for JWK

Brian Campbell <bcampbell@pingidentity.com> Tue, 19 February 2013 23:44 UTC

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From: Brian Campbell <bcampbell@pingidentity.com>
Date: Tue, 19 Feb 2013 16:43:29 -0700
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Subject: [jose] TTL for JWK
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I'd like to float the idea of introducing a time to live parameter to the
base JWK document, which could probably fit in as a subsection of ยง4 that
defines parameters common to all key types [1].

The motivation is that many uses of JWKs will involve caching of JWK data
and a TTL parameter could be used to indicate how long a key could be
safely cached and used without needing to recheck the JWK source. I don't
want it to be a hard expiration date for the key but rather a hint to help
facility efficient and error free caching.

OpenID Connect has a real use case for this where entities publish their
keys via a JWK Set at an HTTPS URL. To support key rotation and encryption,
there needs to be some way to indicate the TTL of a public key used to
encrypt. Of course, this isn't the only way to skin that cat but it strikes
me as a good way and one that might provide utility for JWK in other
contexts.
JSON Web Token [2] defines a data type that is "A JSON numeric value
representing the number of seconds from 1970-01-01T0:0:0Z UTC until the
specified UTC date/time" that seems like it could be co-opted to work well
as the value for a "ttl" parameter.

[1] http://tools.ietf.org/html/draft-ietf-jose-json-web-key-08#section-4

[2] http://tools.ietf.org/html/draft-ietf-oauth-json-web-token-06#section-2