DropBoxLogin

1)
.NET Framework 4.5

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Nemiro.OAuth;
using Nemiro.OAuth.LoginForms;

2)
3)    Well, the part of the code, in which I use this constuction

private void GetAccessToken()
        {
            var login = new DropboxLogin("n1d21hsifzp1ye5", "n1d21hsifzp1ye5", true, true);
            login.Owner = this;
            login.ShowDialog();

            if (login.IsSuccessfully)
            {
                Properties.Settings.Default.AccessToken = login.AccessToken.Value;
                Properties.Settings.Default.Save();
            }
            else
            {
                MessageBox.Show("error...");
            }
        }