The bearer token presented with the proof.
How far iat may be from NowSeconds, either way.
The path the proof must name, matched as a suffix of the proof URL's path. This binds a proof to one
endpoint, so a proof made for another route of the same API cannot be reused here. The origin and any
base path are not compared: one API can be reached under several public origins and base paths (a
proxy, MJAPI_BASE_PATH), and the caller cannot reliably list them. Leaving them open grants nothing,
because only the holder of the bound key can sign a proof, and ath ties the proof to one token.
What the verifier expects of a proof.