Hi,
Yes thats correct.
Have you also added the AD-configuration to the configuration file?: C:\Program Files\ArcGIS\Portal\etc\portal-config.properties
idp.type=WINDOWS
idp.ad.user=domain\\domain_user
idp.ad.userpassword=domainuser_password
idp.ad.user.fullnameattribute=cn
idp.ad.user.emailattribute=mail
idp.userpassword.encrypted=false
You can also check the log and see if you find something interesting
C:\arcgisportal\logs\webserver\catalina.<date>.log:
C:\arcgisportal\logs\webserver\localhost.<date>.log