Authenticate with a registry. Similar to the ``docker login`` command.

        Args:
            username (str): The registry username
            password (str): The plaintext password
            email (str): The email for the registry account
            registry (str): URL to the registry.  E.g.
                ``https://index.docker.io/v1/``
            reauth (bool): Whether or not to refresh existing authentication on
                the Docker server.
            dockercfg_path (str): Use a custom path for the Docker config file
                (default ``$HOME/.docker/config.json`` if present,
                otherwise``$HOME/.dockercfg``)

        Returns:
            (dict): The response from the login request

        Raises:
            :py:class:`docker.errors.APIError`
                If the server returns an error.

def login(self, username, password=None, email=None, registry=None,
              reauth=False, dockercfg_path=None):
        """
        Authenticate with a registry. Similar to the ``docker login`` command.

        Args:
            username (str): The registry username
            password (str): The plaintext password
            email (str): The email for the registry account
            registry (str): URL to the registry.  E.g.
                ``https://index.docker.io/v1/``
            reauth (bool): Whether or not to refresh existing authentication on
                the Docker server.
            dockercfg_path (str): Use a custom path for the Docker config file
                (default ``$HOME/.docker/config.json`` if present,
                otherwise``$HOME/.dockercfg``)

        Returns:
            (dict): The response from the login request

        Raises:
            :py:class:`docker.errors.APIError`
                If the server returns an error.
        """

        # If we don't have any auth data so far, try reloading the config file
        # one more time in case anything showed up in there.
        # If dockercfg_path is passed check to see if the config file exists,
        # if so load that config.
        if dockercfg_path and os.path.exists(dockercfg_path):
            self._auth_configs = auth.load_config(
                dockercfg_path, credstore_env=self.credstore_env
            )
        elif not self._auth_configs or self._auth_configs.is_empty:
            self._auth_configs = auth.load_config(
                credstore_env=self.credstore_env
            )

        authcfg = self._auth_configs.resolve_authconfig(registry)
        # If we found an existing auth config for this registry and username
        # combination, we can return it immediately unless reauth is requested.
        if authcfg and authcfg.get('username', None) == username \
                and not reauth:
            return authcfg

        req_data = {
            'username': username,
            'password': password,
            'email': email,
            'serveraddress': registry,
        }

        response = self._post_json(self._url('/auth'), data=req_data)
        if response.status_code == 200:
            self._auth_configs.add_auth(registry or auth.INDEX_NAME, req_data)
        return self._result(response, json=True)