I grabbed the basic oath sample for the 3.23 API from here: https://developers.arcgis.com/javascript/3/jssamples/portal_oauth_inline.html
set the portal url to our internal Portal for ArcGIS and it worked. Next, I upgraded it to the 4.6 API and now it no longer works. I get no errors in the console, it does redirect to the oath page and allow me to login, but it just does not reload the page afterwards. I tried both inline and popup, same result.