$("#btn_login").click(function () {
    var url = "login";
    var xhr = new XMLHttpRequest();
    xhr.open("POST", url);
    console.log('url:');
    console.log(url);
    xhr.setRequestHeader("accept", "application/json");
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xhr.onreadystatechange = function () {
      if (xhr.readyState === 4) {
        console.log(xhr.status);
        responseOBJ = JSON.parse(xhr.responseText) ;         // error
        console.log(responseOBJ.access_token);
        // document.cookie = 'jwt_token='+responseOBJ.jwt_token    // access_token -> jwt_token
        document.cookie = 'jwt_token='+responseOBJ.access_token; 
        console.log('cookie: ');
        console.log(document.cookie);     // test log
        console.log('登入成功');
        alert('登入成功!!');
        window.location.replace("/home");
      }
    };
    var data = "grant_type=&username=" + $('#username').val() + "&password="+$('#password').val()+"&scope=&client_id=&client_secret=";
    console.log("data:");
    console.log(data);    // test 
    xhr.send(data);
  });