A pairing code another device of the same user can claim (needs a device token).
Sends with the bearer token; on 401 with a refreshable source, retries once with a fresh token.
StaticetagSame as Qt's SyncServerClient::etagFor: the quoted hex SHA-256 of the data.
StaticisStaticselfFor a self-hosted server URL like https://sync.example.org (adds /api/v1, as Qt does).
Exchanges a pairing code for a device token (no token needed; the code is the credential).