Agregar medios con WP-Rest-API v2

Necesito su ayuda para cargar una imagen multimedia en mi blog de wordpress a través de la autenticación Wp-rest-api v2 y Oauth2.

No encontré en la documentación de REST API la forma de enviar mis datos de imagen (nombre del campo, modo de envío ...).

require('OAuth2/Client.php');
require('OAuth2/GrantType/IGrantType.php');
require('OAuth2/GrantType/AuthorizationCode.php');

const CLIENT_ID     = 'XXX';
const CLIENT_SECRET = 'XX';

const REDIRECT_URI           = 'http://127.0.0.1/test_api_wp/test.php';

const AUTHORIZATION_ENDPOINT = 'http://wordpress.local/oauth/authorize';
const TOKEN_ENDPOINT         = 'http://wordpress.local/oauth/token';

$client = new OAuth2\Client(CLIENT_ID, CLIENT_SECRET);

if (!isset($_GET['code']))
{
    $auth_url = $client->getAuthenticationUrl(AUTHORIZATION_ENDPOINT, REDIRECT_URI);
    header('Location: ' . $auth_url);
    die('Redirect');
}
else
{
    $params = array('code' => $_GET['code'], 'redirect_uri' => REDIRECT_URI);
    $response = $client->getAccessToken(TOKEN_ENDPOINT, 'authorization_code', $params); //authorization_code
    $token = $response['result']['access_token'];
    $client->setAccessToken($token);
    $client->setAccessTokenType(OAuth2\Client::ACCESS_TOKEN_BEARER);

}

$values = array(
    "date" => "2015-11-26 10:00:00",
    "date_gmt" => "2015-11-26 09:00:00",
    "modified" => "2015-11-26 10:00:00",
    "modified_gmt" => "2015-11-26 09:00:00",
    "status" => "future",
    "title" => "Titre media",       
    "description" => "description media",
    "media_type" => "image",
    "source_url" => "https://www.base64-image.de/build/img/mr-base64-482fa1f767.png"
);

$data = $client->fetch("wordpress.local/wp-json/wp/v2/media", $values, "POST");
echo "<pre>";print_r($data);echo "</pre>";

La respuesta:

Array
(
    [result] => Array
        (
            [code] => rest_upload_no_data
            [message] => No data supplied
            [data] => Array
                (
                    [status] => 400
                )

        )

    [code] => 400
    [content_type] => application/json; charset=UTF-8
)

¿Alguna idea? Muchas gracias