Can I use IWA authentication to access Portal for ArcGIS without using the ArcGIS Web Adaptor?

It is possible to log in to Portal for ArcGIS using Integrated Windows Authentication (IWA) log-in credentials, without going through the ArcGIS Web Adaptor.

IIS normally performs an initial authentication step, and forwards the log-in information to Portal. The Web Adaptor passes the log-in username to Portal in the format username@DOMAIN. Logging in directly to Portal is possible by changing the usual user login domain\username to the format username@DOMAIN (note that the domain part must be in capital letters). The usual Windows password is used.