ArcGIS Online login flow through JS 3.x

main.js

require([
  'app/config',
  'dojo/ready',
  'dojo/on',
  'dojo/dom',
  'esri/arcgis/OAuthInfo',
  'esri/IdentityManager'],
  function(
  config, 
  ready, 
  on,
  dom,
  OAuthInfo, 
  IdentityManager
  ) {
  checkLogin(config);
  
  function checkLogin(config) {
    IdentityManager.registerOAuthInfos([info]);
    IdentityManager.checkSignInStatus(info.portalUrl + '/sharing')
      .then(loginSuccess)
      .otherwise(loginFail);
  }

  function loginSuccess(credential) {
    console.debug('credential', credential);
    ready(function () {
      // Init the app UI.
      // ...

      on(dom.byId('signOut'), 'click', signOut);
    });
  }

  function loginFail(response) {
    console.debug('Login Failed', response);
    IdentityManager.getCredential(info.portalUrl + "/sharing");
  }

  function signOut() { 
    IdentityManager.destroyCredentials();
    window.location = window.location.origin + window.location.pathname;
  }
});