$.ajax({
    method: "POST",
    url: "https://login.salesforce.com/services/oauth2/token",
    crossDomain: true,
    data: grant_type=password" +
      "&client_id=" + CLIENTID +
      "&client_secret=" + CLIENTSECRET +
      "&username=" + USERNAME +
      "&password=" + PASSWORD,
    dataType: 'jsonp',
    success: function (data) {
        console.log(data);
    },
    error: function (err) {
        console.log(err);
    }
});