save login details on successful login
If we login successfully, save the login data immediately.  That way if users run a second command  before the first one finishes, they only have to login once.
@@ -217,6 +217,7 @@ class Backend:
LOGGER.info("Interactive device authentication succeeded")
print("Login succeeded", flush=True)
+ self.save_cache()
return access_token
def request(
