如何保护浏览器从CSRF攻击中使用的RESTful API ?

I'm designing the API for a group of sites. The sites are very similar (kind of like StackOverflow, SuperUser and ServerFault), and it makes sense for them to have a shared backend. Hence we decided to try and have a nice REST API as a backend, and a bunch of very-similar-but-different frontends consuming said API. The frontends should preferably be all static, but that's not a hard requirement if it turns out to be borderline impossible.I'm designing the API for a group of sites. The