Return the username.

    .. versionadded:: 2017.7.0

    CLI Example - select all devices using `foobar` as username for connection:

    .. code-block:: bash

        salt -G 'username:foobar' test.ping

    Output:

    .. code-block::yaml

        device1:
            True
        device2:
            True

def username(proxy=None):
    '''
    Return the username.

    .. versionadded:: 2017.7.0

    CLI Example - select all devices using `foobar` as username for connection:

    .. code-block:: bash

        salt -G 'username:foobar' test.ping

    Output:

    .. code-block::yaml

        device1:
            True
        device2:
            True
    '''
    if proxy and salt.utils.napalm.is_proxy(__opts__):
        # only if proxy will override the username
        # otherwise will use the default Salt grains
        return {'username': _get_device_grain('username', proxy=proxy)}