您可以使用keycloakSession对象访问请求标头，例如

You can get access to request headers using keycloakSession object, something like

keycloakSession.getContext().getRequestHeaders().getRequestHeader("User-Agent")

如果检查DefaultEvaluationContext类的代码，这就是它们添加User-Agent标头的方式.

If you check the code for DefaultEvaluationContext class, that is how they add the User-Agent header.