This might shed some light on the issue
Connecting Azure web app service (.net8) to SSRS on Azure VM by using private DNS
Billey
10
Reputation points
My azure web app service(.net8) connect to SSRS on VM by using the private DNS name provided by Azure to the VM,
but my credentials did not work when I run the report on my azure web app server.
The private DNS name works fine with my credentials via url I can hit the SSRS reports server through a browser.
Did I miss something to allow the credentials to work on azure web app service?
Regarding the rsreportserver.config, our reporting service use the AuthenticationTypes = RSWindowsNTLM but our Azure VM did not have domain.