@Override
            public void handle(Request request, Response response) {
                String user = request.queryParams("user");
                String password = request.queryParams("password");

                String dbPassword = usernamePasswords.get(user);
                if (!(password != null && password.equals(dbPassword))) {
                    halt(401, "You are not welcome here!!!");
                }
            }
Example showing a very simple (and stupid) authentication filter that is
executed before all other resources.
When requesting the resource with e.g.
http://localhost:4567/hello?user=some&password=guy the filter will stop the
execution and the client will get a 401 UNAUTHORIZED with the content 'You
are not welcome here'
When requesting the resource with e.g.
http://localhost:4567/hello?user=foo&password=bar the filter will accept the
request and the request will continue to the /hello route.
Note: There is also an "after filter" that adds a header to the response

@author Per Wendel
src/test/java/spark/examples/filter/FilterExample.java