When you configure a Resource URL and you go to Jenkins configure page the checkUrl of the ResourceDomainConfiguration tries to reach the instance-identity/ path on the resource url. But this url is not in the allowed path of the ResourceDomainFilter

As a result a 404 is returned and all the code for status 200 is basically unreachable.

When using using jetty it falls back to reading the responseMessage for the specific error message. 

When running on tomcat the responseMessage is not set at all it seems and we run into a NPE which breaks the UI (save is still working just an ugly error is shown below the resource root url input field)

The fix in JENKINS-62133 was obviously not complete for all cases.

Ideally the instance-identity path is allowed in the filter