How to resolve Ajax error No 'Access-Control-Allow-Origin' header is present on the requested resource'

Question

I am trying to get token from drchrono.com. But I get following error. Can somebody please help me how to solve this?

Error

Access to XMLHttpRequest at 'https://drchrono.com/o/token/' from origin 'null' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

Method

function getToken() {
    var authData = {};
    authData.code = $("#txtCode").val();
    authData.grant_type = "authorization_code";
    authData.redirect_uri = "https://test.com/WebForm1.aspx";
    authData.client_id = "asdfasdfadfassdfasddfdsaf";
    authData.client_secret = "asdfasdfasdfasfasfasdfsafsadfsadf";

    var jsonAuthData = window.JSON.stringify(authData);
    var authDataUri = "https://drchrono.com/o/token/";
    $.ajax({
        type: "POST",
        contentType: "application/json; charset=utf-8",
        datatype: "json",
        url: authDataUri,
        data: jsonAuthData,
        async: true,
        crossDomain: true,
        headers: {
            'Access-Control-Allow-Origin': '*'
            //'Access-Control-Allow-Origin': 'https://test.com/WebForm1.aspx'
        },
        beforeSend: function (XMLHttpRequest) {
        },
        success: function (data, textStatus, XmlHttpRequest) {
            console.log(data);
        },
        error: function (XMLHttpRequest, textStatus, errorThrown) {
            console.log(XMLHttpRequest);
            console.log(textStatus);
            console.log(errorThrown);
        }
    });
}