[Backport 3.1] JAAS security fails behind a proxy injecting the context path when the HstFilter is configured with <dispatcher>FORWARD</dispatcher> as well

When the HstFilter in the web.xml is

  <filter-mapping>
    <filter-name>HstFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
  </filter-mapping>

instead of normally

  <filter-mapping>
    <filter-name>HstFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
  </filter-mapping>

then, in case of a JAAS login behind a proxy, the login fails and ends with a URL /site/login/resource

The reason is that the internal container security constraint on /login/resource forwards the request, but now the HstFilter listens to FORWARDS as well, and in the HstDelegateeFilterBean, this triggers a response with a redirect. After this redirect, again a redirect happens triggering j_security_check, which triggers a redirect to a URL starting with /site (also behind a proxy) that is not followed any more by another redirect.

The solution is, that the HstFilter should do chain.doFilter on requests that are a security request and that happen to be a forward.