Service URL carrying a short-lived token, refreshed as it nears expiry.
Accessors are async because a refresh is a network call.
class ServiceUrlThe browser URL that authenticates then redirects, refreshed if near expiry.
ISO 8601 expiry of the current token, refreshed if near expiry.
Fetch a path on the service with the token header injected.
The service base URL, refreshed if near expiry.
The signed token, refreshed if near expiry.