uiwebview - iOS网页请求如何带上cookie

想在ios的uiwebview请求中带上额外的cookie，网上搜了下都是这样的：

        let cookie = NSHTTPCookie(properties: [
            NSHTTPCookieName:"username",
            NSHTTPCookieValue:"test",
            NSHTTPCookiePath:"/",
            NSHTTPCookieDomain:"http://localhost/test/",
            ]);
NSHTTPCookieStorage.sharedHTTPCookieStorage().setCookies([cookie!], forURL: NSURL(string: "http://localhost/test/")!, mainDocumentURL: nil)

但是我设置之后，在服务端用php打印cookie，没有任何cookie信息，请问还要怎么设置？