Reporting Services – Host header and Windows Authentication

SQL 2016 – Enterprise Edition
Windows 2016
Reporting Services runs on domain account (SPN registered for new host header)

Problem:
When adding a host header in Reporting Services Configuration tool, like reports.server.net, users need to login to the reporting services.
When I remove the host header and try to connect to hostname/reports I do not get prompted for user/password.

Fact:
– When i use the default site address http://servername/Reports, before adding a new host header, the site opens up without login prompt

What I've done:

• Created a Host record in DNS for the new address, pointing at reporting services server
• Registered a SPN for the new host record to the service account for reporting service
• Added the new host header to reporting services for web service url and web portal url
• Played around authentication types in the reportserver.config file according to (https://docs.microsoft.com/en-us/sql/reporting-services/security/configure-windows-authentication-on-the-report-server?view=sql-server-ver15&viewFallbackFrom=sql-server-ver13)
• Enabled delegation for the reporting services service account "just in case"

I can't seem to add a host header without beening forced to login, despite above.

Anyone been here?