Repeated prompts to sign in when accessing a Portal for ArcGIS website configured with IWA

Description

When attempting to log in to a Portal for ArcGIS website configured with Integrated Windows Authentication (IWA), the login fails, and prompts the user to sign in with Windows credentials. The sign-in prompt is continuously returned, and the Portal for ArcGIS home page does not load despite entering the correct Windows credentials.

The following error message is returned in the developer tools console:

Error:   
401 Unauthorized

This issue persists despite the following conditions being true:

• Windows Authentication is enabled in the machine's Internet Information Services (IIS) Manager.
• Anonymous authentication is disabled.
• The 443 binding in IIS Manager does not have a hostname assigned, and the binding has a valid CA-signed certificate.

Cause

The organization's domain controller is not responding to Active Directory authentication and replication.

Solution or Workaround

Restart the organization's domain controller. This process must be performed by the organization's IT and Active Directory administrators.