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