Slack object method function to construct and execute on the API URL.

    :param api_key:     The Slack api key.
    :param function:    The Slack api function to perform.
    :param method:      The HTTP method, e.g. GET or POST.
    :param data:        The data to be sent for POST method.
    :return:            The json response from the API call or False.

def query(function,
          api_key=None,
          args=None,
          method='GET',
          header_dict=None,
          data=None,
          opts=None):
    '''
    Slack object method function to construct and execute on the API URL.

    :param api_key:     The Slack api key.
    :param function:    The Slack api function to perform.
    :param method:      The HTTP method, e.g. GET or POST.
    :param data:        The data to be sent for POST method.
    :return:            The json response from the API call or False.
    '''

    ret = {'message': '',
           'res': True}

    slack_functions = {
        'rooms': {
            'request': 'channels.list',
            'response': 'channels',
        },
        'users': {
            'request': 'users.list',
            'response': 'members',
        },
        'message': {
            'request': 'chat.postMessage',
            'response': 'channel',
        },
    }

    if not api_key:
        api_key = __salt__['config.get']('slack.api_key') or \
            __salt__['config.get']('slack:api_key')

        if not api_key:
            log.error('No Slack api key found.')
            ret['message'] = 'No Slack api key found.'
            ret['res'] = False
            return ret

    api_url = 'https://slack.com'
    base_url = _urljoin(api_url, '/api/')
    path = slack_functions.get(function).get('request')
    url = _urljoin(base_url, path, False)

    if not isinstance(args, dict):
        query_params = {}
    else:
        query_params = args.copy()
    query_params['token'] = api_key

    if header_dict is None:
        header_dict = {}

    if method != 'POST':
        header_dict['Accept'] = 'application/json'

    result = salt.utils.http.query(
        url,
        method,
        params=query_params,
        data=data,
        decode=True,
        status=True,
        header_dict=header_dict,
        opts=opts
    )

    if result.get('status', None) == salt.ext.six.moves.http_client.OK:
        _result = result['dict']
        response = slack_functions.get(function).get('response')
        if 'error' in _result:
            ret['message'] = _result['error']
            ret['res'] = False
            return ret
        ret['message'] = _result.get(response)
        return ret
    elif result.get('status', None) == salt.ext.six.moves.http_client.NO_CONTENT:
        return True
    else:
        log.debug(url)
        log.debug(query_params)
        log.debug(data)
        log.debug(result)
        if 'dict' in result:
            _result = result['dict']
            if 'error' in _result:
                ret['message'] = result['error']
                ret['res'] = False
                return ret
            ret['message'] = _result.get(response)
        else:
            ret['message'] = 'invalid_auth'
            ret['res'] = False
        return ret