Use the documentation for Portal's AD and PKI setup and ensure to set ArcGIS for Server to HTTP/HTTPS.<a href="http://server.arcgis.com/en/portal/latest/administer/windows/using-windows-active-directory-and-pki-to-secure-access-to-your-portal.htm" target="_blank">http://server.arcgis.com/en/portal/latest/administer/windows/using-windows-active-directory-and-pki-to-secure-access-to-your-portal.htm</a>