Authenticated URL for accessing an HTTP service running in a sandbox.
Properties auto-refresh the token transparently when it nears expiry.
HTTP helper methods (.get, .post, etc.) inject the auth header
automatically.
When constructed by :meth:SandboxClient.service or
:meth:Sandbox.service, the object holds an internal refresher that
re-calls the API to obtain a fresh token before the current one expires.
Example::
svc = sb.service(port=3000)
resp = svc.get("/api/data") # token injected + auto-refreshed
print(svc.browser_url) # always-fresh URL
