Consider a counter for signing. `cnt`

[zamicol]

A simple integer counter field named cnt. Useful for rotation policies and other key hygiene.

{
 "alg":"ES256",
 "now":1623132000,
 "kid":"Zami's Majuscule Key.",
 "prv":"bNstg4_H3m3SlROufwRSEgibLrBuRq9114OvdapcpVA",
 "tmb":"cLj8vsYtMBwYkzoFVZHBZo6SNL8wSdCIjCKAwXNuhOk",
 "pub":"2nTOaFVm2QLxmUO_SjgyscVHBtvHEfo2rq65MvgNRjORojq39Haq9rXNxvXxwba_Xj0F5vZibJR3isBdOWbo5g",
  "cnt": 7
}

This probably belongs in extended and not core.