function form_send()
{
	var frm = document.forms.auth;
	...
	event.preventDefault();
	var login = frm.login.value;
	var password = frm.password.value;
	var hash = hexMD5(password);
	var auth = {"username": login, "hash": hash};
	http('/auth', auth,
		function(data)
		{
			...
			http('/login', {"username": login, "password": password},
				function(data)
				{
					...
				},
				function(err)
				{
					...
				}
			);
		},
		function(err)
		{
			...
		}
	);
}

function http(path, data, success, fail)
{
	var xhr = new XMLHttpRequest();
	var uri = '...';
	...
	xhr.open("POST", uri, true);
	xhr.onreadystatechange = function() {
		if (this.readyState != 4) return;
		if (this.status != 200)
		{
			fail('#'+this.status + ' ' + this.statusText);
			return;
		}
		success(res)
		return res;
	};
	xhr.send(data);
}

	var frm = document.forms.auth;
	var mode = frm.mode.value;
	var btn = frm.querySelector('button[type="submit"]');
	var tag = frm.querySelector('button[type="submit"] ~ .tag');