open_async
Description:
public static async Session open_async (Slot slot, SessionOptions options, TlsInteraction? interaction, Cancellable? cancellable) throws Error
  
  Open a session on the slot.
This call will return immediately and complete asynchronously.
Parameters:
| slot | the slot to open session on | 
| options | session options | 
| interaction | optional interaction for logins or object authentication | 
| cancellable | optional cancellation object | 
| callback | called when the operation completes | 
| user_data | data to pass to callback |