CspInterceptor reportUri with context

At the moment the reportURI has to start with a schema (http, https) or with "/". But how can i add the context to the url?

Example:

Action: /report.action

Application running in context "showcase".

Complete URL: http://example.com/showcase/report.action

That means, that in the configuration i have to set reportUri = /showcase/report.action. But the context should not be hardcoded in struts.xml

Is there a parameter for the context?

I would prefer the solution from ServletRedirectResult: an option to add the context (PrependServletContext)