Status code for processing handler but not invoking resource

In the Servlet Container Profile of JASPIC the ServerAuthModule.validateRequest method can return the SUCCESS} status code, which means the given handler should be processed by the JASPIC runtime and the requested resource should be invoked. This same method can also return {{SEND_CONTINUE which means the handler should not be processed and the resource should not be invoked.

Neither of those status codes address the use case where a SAM wishes authentication to happen first (and ask the container to remember this) and then immediately redirect to a new resource.

This happens for instance when the user tries to access protected resource /A after which the SAM redirects the user to an external authentication provider at [http://example.com](http://example.com) which then redirects the user back to a general resource at /return which the SAM is monitoring. The SAM could redirect to /A first and then do authentication, but this slightly complicates the logic that needs to be coded.

Fragment of code from an actual SAM demonstrating a similar case:

```
if (...) {
// [...]

if (authenticated) {

String savedURL = getSavedURL(request);
// [...]

// Note: JASPIC doesn't really support authenticating AND redirecting during the same request,
// so we need to redirect first and then finally do the authentication with the container on
// the request we redirected to.
redirect(response, savedURL);
return SEND_CONTINUE;
} else {
// [...]
}

} else if (isOnOriginalURLAfterAuthenticate(request)) {

Authenticator authenticator = getSavedAuthenticator(request);
```

[Source](https://github.com/arjantijms/two-factor-sam/blob/master/src/main/java/net/eisele/glassfish/twofactorsam/TwoFactorServerAuthModule.java#L110)

For completeness and to make some flows easier to code, I'd like to suggest the introduction of a new status code, something like SUCCESS_SEND_CONTINUE, meaning:

* Process the handler and any directives put into the MessageInfo map (such as asking the container to remember the auth session)
* Don't invoke the resource