OptionalcloudOptionalcontextRequest context. Omitted by default (iOS).
OptionalscreenScreen instance id (<name>:<index>) the send_login_request response issued
for this screen. The app opens the screen the response told it to, so the id
is read back from that parsed response; when absent a fresh id is generated
for platforms whose response carries none.
OptionalurlOverride the relative URL. The host comes from the platform host policy and context.
When set, sends
cloud_trust_tokeninclient_input_params(Android sendsnull).