I created a WAB application on arcgis online and I downloaded and deployed this application on my iis server.
I then configured with a proxy (user / password) and everything works fine. No need to enter a user / password.
The only problem is that all the thumbnails in basemapgallery is not visible. I receive a 403 error when downloading ... http: //xxx.maps.arcgis.com/sharing/rest/content/items/xxx/info/thumbnail/xx.png
Does anyone have a solution?