function checkAuth() {
    gapi.auth.authorize({
        'client_id': CLIENT_ID,
        'scope': SCOPES.join(' '),
        'immediate': true
    }, handleAuthResult);
}

//authorize apps
function handleAuthClick(event) {
    gapi.auth.authorize(
          { client_id: CLIENT_ID, scope: SCOPES, immediate: false },
          handleAuthResult);
    return false;
}

//check the return authentication of the login is successful, we display the drive box and hide the login box.
function handleAuthResult(authResult) {
    if (authResult && !authResult.error) {
        $("#drive-box").show();
        $("#drive-box").css("display","inline-block");
        $("#login-box").hide();
        showLoading();
        getDriveFiles();
    } else {
        $("#login-box").show();
        $("#drive-box").hide();
    }
}