code: def basic_auth(credentials):
      
      encoded = b64encode(':'.join(credentials).encode('ascii')).decode()
      return header_adder({'Authorization': 'Basic ' + encoded})
docs: Create an HTTP basic authentication callable
  
      Parameters
      ----------
      credentials: ~typing.Tuple[str, str]
          The (username, password)-tuple
  
      Returns
      -------
      ~typing.Callable[[Request], Request]
          A callable which adds basic authentication to a :class:`Request`.