But, if the boards are inaccessible, surely the links are as well...? (Unless you mean they're shown in the sidebar even though one gets a "Board doesn't exist" error...?)
No...
Right now if you can see a board, you get the RSS feed as you should. But that wasn't what I suggested doing. I was suggesting hiding the RSS links if the board is not visible to guests. If the board is not accessible to guests, there's no need for RSS feeds as it currently stands.
Obviously, we'd have to reload the user yes.
Well, that's the thing. We can either fully reload the user, or we can intercept the request and attempt to load the user up front if that makes sense.
Which implies that one would want to supply Google with their username & password for a site...? I certainly wouldn't. But I would be perfectly fine with providing it a custom key for reading private boards. As long as no one at Google can actually get access to my account with it...
Of course they can. It's inserted in plain text in the URL as standard...
Well, the session is loaded, the user account updated, but the main online log won't be. Since the session is loaded up front, even PHPSESSID sessions are invoked.