How can I get the access token of the user logged in using widget in ringcentral?

I'm using the ringcentral embeddable widget using the following code.

(function() {
    var rcs = document.createElement("script");
    rcs.src = "https://ringcentral.github.io/ringcentral-embeddable/adapter.js?clientId={client_id}&appServer={app_server}&redirectUri={redirect_uri}";
    var rcs0 = document.getElementsByTagName("script")[0];
    rcs0.parentNode.insertBefore(rcs, rcs0);
  if (window.RCAdapter) {
    window.RCAdapter.setMinimized(false);
  }
})();

I want to store the token, refresh token and user id after a successful login. Can someone please help in how can I get the above details if I'm just using the ringcentral widget?