RFE: enable expiry warnings before expiry

[jku]

In https://github.com/jku/tuf-demo I would like an easy way to create GitHub issues some time before metadata expires: this applies to especially root, but but maybe also targets metadata

Not sure how this should work but possibly tufrepo verify could have an option that fails if expiry is less than x days in the future?

[joshuagl]

go-tuf very recently added a status command in theupdateframework/go-tuf@af3c7d6
which lets you call: tuf status --valid-at "$(date -d '+1 hour')" timestamp

[jku]

yes, something like that which can then be used (for example) in a workflow in the metadata repository to create a GitHub issue if it fails.

The remaining extra bit is tying keys to identities like github accounts. I suppose we could add a "x-tufrepo-key-owner-github" field to keys so the GitHub issue could then name the correct owner... or something. I'm tempted to just use github username as keyname

But just the validity check would be good