(1) Connect to portaladmin > Security > Config.
(2) Update Security Configuration. Change enableAutomaticAccountCreation to true.
(3) Ensure that Web Adaptor for portal is configured for Windows Authentication.
(4) Log into a system with the s-test account.
(5) Access the Portal Home and allow Portal to create the account. This creates the account with the correct username.
(6) Update Security Configuration. Change enableAutomaticAccountCreation to true.
Authentication is now successful.