OptionalaudThe Command to eventually invoke
Expiration UTC Unix Timestamp in seconds (valid until)
Issuer DID (sender)
OptionalmetaMeta (asserted, signed data) — is not delegated authority
Optionalnbf"Not before" UTC Unix Timestamp in seconds (valid from)
The nonce of the UCAN
OptionalsubPrincipal that the chain is about (the [Subject])
Audience DID (receiver)