How to get a username from a userId?

I'm making a global leaderboard and so far everything works except for displaying the players username, as it just shows the userId of the player (which is the key in my ordered data store).

name = game:GetService("HttpService"):GetAsync("http://api.roblox.com/Users/"..string.sub(id,6),false)

I know that this cannot work as it is accessing a subdomain of ROBLOX but I have no idea how else to do it. I've tried using a proxy I saw mentioned on a few other threads but I get a CURL error: Couldn't resolve host name.

Can anyone help?