def authentication_requests(key_handles)
      key_handles = [key_handles] unless key_handles.is_a? Array
      key_handles.map do |key_handle|
        SignRequest.new(key_handle)
      end
    end
def authentication_requests(key_handles)
      key_handles = [key_handles] unless key_handles.is_a? Array
      key_handles.map do |key_handle|
        SignRequest.new(key_handle)
      end
    end
* *Args*:
   - +app_id+:: An application (facet) ID string


 Generate data to be sent to the U2F device before authenticating

 * *Args*:
   - +key_handles+:: +Array+ of previously registered U2F key handles

 * *Returns*:
   - An +Array+ of +SignRequest+ objects