Default AttestoPhoenix.CIBAPing deliverer, built on Req.
POSTs {"auth_req_id": ...} as application/json to the client's registered
backchannel_client_notification_endpoint with
Authorization: Bearer <client_notification_token> (OpenID Connect CIBA Core
1.0 §10.2). Redirects and retries are disabled and the timeout is short:
notification delivery is best-effort and must never let a slow or hostile
client stall the OP - the tokens are already available at the token endpoint,
and a client that misses the ping falls back to polling.
A 2xx (200/204) is success; anything else (a non-2xx status - including the 401/403 the suite's non-retry module returns, or a 3xx that must NOT be followed - or a transport error) is reported so the caller can log it and move on.
Req is an optional dependency. A host that enables CIBA ping mode with the
default deliverer must have :req available; one that supplies its own
ciba: [ping_http_client: ...] does not.