[TLS] Relative vs absolute ServerConfiguration.expiration_date

[Blake Matheny <[e-mail]>]

One of the topics of discussion at the WG discussion was whether ServerConfiguration.expiration_date should be an absolute or relative value. Subodh (CC) dug into our production data and found that nearly half of the TLS errors we see in production (end user to edge/origin) are due to date mismatch. This often occurs when people intentionally reset the clock on their phone, or for other various reasons.

Due to the high rate of date mismatch errors we see, my preference would be that ServerConfiguration.expiration_date be a relative value instead of an absolute one. This provides the client an opportunity to correctly use a monotonic (or other similar) clock to minimizing exposure, without losing the value of the ServerConfiguration. Using an absolute value means that ServerConfiguration, for clients with invalid clocks, would essentially never be cacheable. These clients wouldn’t benefit from ServerConfiguration.

Thoughts or feedback?

-Blake