I have an ASP.NET / MVC website using Windows Authentication. On IIS side, it is set-up to only allow Windows Authentication. enter image description here [https://i.stack.imgur.com/nsm1q.png] The web.config side is configured to allow windows authentication only: <authentication mode="Windows" /> <authorization> <allow verbs="OPTIONS" users="*" /> <deny users="?" /> </authorization> <identity impersonate="true" [...] read more