format, use, issuer, identifier (all required),
and optionally expiresAt, clientId, subject, request and
keepBelow
a promise of { ok: true, claim }, or { ok: false, reason }
where reason is replay (with existing), full or store
Records that a document has been accepted, unless it already was.
With a request the row is reserved and bound to the response: a status below
keepBelow(300 by default) spends it, anything else releases it. Without one it is spent at once. A store that cannot be asked fails closed.