Asset Selector is an AEM Assets interface that displays AEM assets. It is set up as a URL (http://<host>:<port>/aem/assetpicker). You can integrate it with your HTML page through an iframe, a pop-up window, or a new tab. Asset Selector interacts with your web page using the HTML5 Window.postMessage communication protocol. For details, see The Window.postMessage method and Cross-document messaging. Asset Selector uses the following structure (response object) to send data and actions (such as Done, Cancel, and so on).
For detailed info refer to http://blogs.adobe.com/contentcorner/2016/03/03/integrating-aem-asset-selector-with-your-web-page/
Authentication is out of scope of Asset Selector. Like any other AEM page, accessing the asset selector page will also redirect the user to the default AEM login page (or any other authentication page used by user to log in to AEM instance )