Do not compute CSP header until it's actually needed #26254
Description
What feature do you want to see added?
Reported in jenkinsci/customizable-header-plugin#315, some CSP extension points do excessive amounts of work and can slow down Jenkins.
This was not a potential problem I had considered in #23915 and so Jenkins still computes the value in CspFilter. This should be improved so that setting the headerName system property can be a viable workaround for such cases.
Upstream changes
No response
Are you interested in contributing this feature?
Fixed locally