Add API identifier data in user_metadata

function (user, context, callback) {
    user.user_metadata = user.user_metadata || {};
    var audience = '';
    audience = audience ||
        (context.request && context.request.query && context.request.query.audience) ||
        (context.request && context.request.body && context.request.body.audience);

    if (audience === '[API identifier]') {
        user.user_metadata.apis = audience;

        // persist the user_metadata update
        auth0.users.updateUserMetadata(user.user_id, user.user_metadata)
            .then(function () {
                callback(null, user, context);
            })
            .catch(function (err) {
                callback(err);
            });
    }

    return callback(null, user, context);
}