private void Login_Click(object sender, EventArgs e)
        {
            //登录参数
            string userName = Username.Text;
            SecureString password = securestring(Password.Text);  
            password.MakeReadOnly();
            //SqlCredential  提供了更安全的方式来指定使用 SQL Server 身份验证的登录尝试密码。 
            SqlCredential credential = new SqlCredential(userName, password);
            //数据库连接
            using (SqlConnection conn = new SqlConnection("Server=(local);Initial Catalog=DATABASE;"))
            {
                conn.Credential = credential;
                conn.Open();
                MessageBox.Show("连接成功");
                conn.Close();
            }
        }
        /// <summary>
        /// 保密文本
        /// </summary>
        /// <param name="text">保密的字符串</param>
        /// <returns></returns>
        private SecureString securestring(string text)
        {
            char[] pChar = text.ToCharArray();

            SecureString password = new SecureString();

            foreach (char c in pChar)
            {

                password.AppendChar(c);

            }
            return password;
        }