The steam Auth API only pulls information found here: https://developer.valvesoftware.com/wiki/Steam_Web_API#GetPlayerSummaries_.28v0001.29
More info about the API can be found here: http://steamcommunity.com/dev
It does a check using the OpenID protocol and then allows you to pull the above from said user.. Which includes, but is not limited to, current steam name, player id, avatar (various sizes), real name (if set), etc.. At no time is there ever any sort of mention or relation to the passwords for these kind of things. You authenticate on steam's website and the password stays there.. Steam just sends our website (or another website) a token that says "He wrote the right pass, let him pass".
So no, your steam information can never, ever, ever be compromised if we get hacked.. Considering we never get any login details from your account.