session.go
func (s *Session) GetOnce(name interface{}) interface{} {
	if x, ok := s.Session.Values[name]; ok {
		s.Delete(name)
		return x
	}
	return nil
}
func (s *Session) GetOnce(name interface{}) interface{} {
	if x, ok := s.Session.Values[name]; ok {
		s.Delete(name)
		return x
	}
	return nil
}
// GetOnce gets a value from the current session and then deletes it.