code: def _get_connection(host, username: str, key_path: str) \
          -> paramiko.Transport or None:
      
      if not username:
          username = shakedown.cli.ssh_user
      if not key_path:
          key_path = shakedown.cli.ssh_key_file
      key = validate_key(key_path)
      transport = get_transport(host, username, key)
  
      if transport:
          transport = start_transport(transport, username, key)
          if transport.is_authenticated():
              return transport
          else:
              print("error: unable to authenticate {}@{} with key {}".format(username, host, key_path))
      else:
          print("error: unable to connect to {}".format(host))
  
      return None
docs: Return an authenticated SSH connection.
  
      :param host: host or IP of the machine
      :type host: str
      :param username: SSH username
      :type username: str
      :param key_path: path to the SSH private key for SSH auth
      :type key_path: str
      :return: SSH connection
      :rtype: paramiko.Transport or None