I'm using vibe.d's sessions for the first time, but having trouble
getting them to work.

When I set up my HttpServerSettings, I include this:

settings.sessionStore = new MemorySessionStore();

And then in my request handler, I have this:

writeln(req.session is null);
if(req.session is null)
    req.session = res.startSession();

I have cookies enabled in my browser, and I can verify that my browser
is properly sending back the correct cookie the server gave it. But
then 'req.session' is still null and a new session gets created.