function prueba() {
$.ajax({
    url: "webserv",
    type: "POST",
    data: {username: "user", password: "pass"},
    dataType: "xml",
    contentType: "aplication/xml; charset=utf-8",
    success: function (resp) {
        console.log(resp);
    },
    error: function () {
        alert("Do!");
    }
});