This is the same as any other scam or phishing deal, common sence prevails in anything like this.
Why would Steam need your account details, since in order to get Steam Friends etc working you have to be logged in, they already have your details.
This is no different from any other kind of scam like this, why would your own bank ring you and ask for your account details, or credit card company, or Steam.
Never ever give any personal details out, ever. No one else ever needs to know them
