The service client id.
The service client secret (from the Keycloak admin console).
OptionalfetchOverride for fetch (tests).
Optionalinit: RequestInitOptionalinit: RequestInitGateway origin, e.g. https://kiban.example.
OptionalrealmRealm name; defaults to kiban.
Configuration for createServiceCredentials: the app's confidential service client (one of
KIBAN_SERVICE_CLIENTS) and the gateway it authenticates against.