Returns the Verifiable Credential Presentation of an x401 handoff created without return_uri, once the End-User completes the flow. The End-User may take several minutes (identity verification). Poll no faster than the Retry-After header of a 202 response. A pending result expires after one hour, a completed result five minutes after completion. Only the End-User of the access token that created the handoff can read the result; any other caller receives 404.