def METHOD_NAME(self, url):
    """Retrieve the authentication strategy for a specified URL.
    :param str url: The full URL you will be making a request against. For
        example, ``'https://api.github.com/user'``
    :returns: Callable that adds authentication to a request.
    .. code-block:: python
        import requests
        a = AuthHandler({'example.com', ('foo', 'bar')})
        strategy = a.get_strategy_for('http://example.com/example')
        assert isinstance(strategy, requests.auth.HTTPBasicAuth)
    """
    key = self._key_from_url(url)
    return self.strategies.get(key, NullAuthStrategy())