I am currently building a web app which requires a user to log in. After they log in, they can see the content they've added to the web app, and things that the web app has done with the content they added.

The URL structure won't differentiate different users (e.g. all user's 'homepage' would be example.com/home, not something like example.com/username/home). This is much the same way that Facebook works (all FB user's messages are at facebook.com/messages, for example).

This presents a problem with advertising. I know that you can use AdSense behind a login, but as far as I'm aware, that's for things like forums, where everyone sees the same things (which wouldn't be the case in this site). I also know that I could put AdSense on the pages without allowing it to log in, which would produce inferior ads. I'm fairly certain it would be against the Terms of Service to give AdSense a login to a 'dummy' account with typical content, as it would not be seeing the same thing as every other user (which is impossible, as they all see different things).

So, my question is: Is there an ad network, or other method, that can serve ads behind a login, maybe based on keywords rather than content?