See my discussion here: https://community.esri.com/thread/215959-how-do-we-smooth-out-the-self-hosted-wab-app-and-the-oauth-... for details... but essentially when you self-host WAB apps that connect to secure portal webmaps, the user is forced to jump thru a lot of login dialogs. This can be simplified by changing the portal mode from "pop-up" to "in-page" but that setting is hard-coded in the tokenUtils file. A simple extra true/false setting in the config could allow for this to be changed.
