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.
The URL to load in an iframe, refreshed if near expiry. The token rides
the URL fragment, so no server sees it; append &redirect=/path to open a
page other than /. Only pages on embedOrigins may frame it.
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.