Generate Random String and Convert To Base64 C# .Net (Dot Net)

 /// <summary>
        /// Generates a random string and converts to base64
        /// </summary>
        /// <returns></returns>
        private string GenerateNewToken()
        {
            Random rand = new Random();
            string randStr = "";
            while (randStr.Length <= 40)
            {
                randStr += rand.Next(0, 255).ToString();
            }
            var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(randStr);
            return System.Convert.ToBase64String(plainTextBytes);
        }