Optional exp field to be honoured by verifiers

[pvillela]

Following is a use case for issuing SHCs that have an expiration date. Country X needs to issue SHC vaccination certificates (visitor vaccination passes) to foreign visitors for their use while in the country. The visitor vaccination certificate is issued based on document(s) from the visitor's country of residence presented by the visitor to Country X. While there may be reasonable protocols for verification of the authenticity of the source information, Country X may not want to vouch for the validity of the information on the visitor pass for an unlimited period of time. For example, if at some point after the visitor has left Country X, there is reason for questioning or revoking the document that was used as the source for the visitor pass, then it could be very hard for Country X to learn about the problem and/or revoke the visitor pass. As a result, the visitor pass based on questionable information would continue to be valid.

An optional exp field to designate the expiration date for an SHC would address the above use case. Verifiers would be required to honour the expiration date and reject SHCs with an exp value before the current date-time.

[jmandel]

Agree that documenting an optional field would be useful, along with commentary that we don't expect it to be routinely used when clinical data SHCs are issued by an authoritative source. Any chance you want to draft a PR @pvillela ?

[pvillela]

I have created PR $214.