SOCKS5 Proxy Authentication in Google Chrome Extension

I'm trying to create a extension which would use my SOCKS5 proxy with authentication. Code in my background script is like this:

var config = {
    mode: "fixed_servers",
    rules: {
        fallbackProxy: {
            scheme: "socks5",
            host: "myhostaddress"
        }
    }
};
chrome.proxy.settings.set(
    { value: config, scope: 'regular' },
    function () { });

chrome.webRequest.onAuthRequired.addListener(
    function (details) {
        console.log("onAuthRequired!", details);
        return ({
            authCredentials: {
                'username': "uname",
                'password': "pass"
            }
        });
    },
    { urls: ["<all_urls>"] },
    ['blocking']
);

But I always get ERR_SOCKS_CONNECTION_FAILED error on each page... What am I doing wrong?