Node＆Express + jQuery：验证会话后保存

I managed to make the user able to authenticate using name/pass. What I'm trying to achieve is, a disabled dropdown, when he authenticates, it gets enabled, then he can access files through the dropdown list. All of that I managed to make, one thing I'm puzzled with is how can I check if he already authenticated or not? So no one would inspect the html code and get access to the files.I managed to make the user able to authenticate