I'm in the process of using the facebook javascript sdk to provide user login functionality for a website.

What I'd like to do is simply take the logged in user's unique facebook id and then put/fetch data to/from a mysql database using the id to determine what data is available to said user.

However I don't really feel like this is very secure. Whilst I'm not storing anything sensitive like credit-card details etc, I'd obviously prefer it to be as secure as practically possible. 

My fear is that with javascript being what is it, someone could fake the facebook id and just pull whatever they wanted.

I'm aware that the php sdk would provide a solid solution to this problem, but i like the javascript one mainly because it's easy to use and I have the basis of it set up (I admit it, I'm lazy).

So, my questions are:

1. Would this set up be as insecure as I feel it might be?
2. Is there anything I can do to improve the security of such a system, other than switching to the php sdk?

Thanks!