OptionalauthOptionalbaseBase URL prepended to relative request paths.
OptionalfetchInjectable for tests.
OptionalheadersExtra headers merged into every request (e.g. a versioning header source).
OptionaltimeoutPer-request timeout (ms). Off by default so long-running upstream calls are never cut short unexpectedly; set it to opt in. Pass 0 to disable explicitly.
Auth strategy; its headers are merged into every request.