index.js

module.exports = function() {
    var authenticated = window.localStorage.getItem('auth_token');
    if (authenticated){
        evolv.context.update({'auth':'true'})
    } else {
        evolv.context.update({'auth':'false'})
    }
};

package.json

{
  "name": "evolv-ebay-authenticated-audience",
  "version": "1.0.0",
  "main": "index.js"
}