Unique Login

UniqueLogin.cs

    public class OnlineInfo
    {
        private static readonly string CurrentSessionId = HttpContext.Current.Session.SessionID;

        public static string CurrentUserName { get; set; }

        /// <summary>
        /// Key:SessionID,Value:UserName
        /// </summary>
        public static Dictionary<string, string> List
        {
            get => (Dictionary<string, string>)HttpContext.Current.Application["Online"] ??
                   new Dictionary<string, string>();
            set
            {
                HttpContext.Current.Application.Lock();
                HttpContext.Current.Application["Online"] = value;
                HttpContext.Current.Application.UnLock();
            }
        }

        public static bool IsOnline => List.ContainsKey(CurrentSessionId) && List[CurrentSessionId] != "OffLine";

        public static bool HasKey => List.ContainsKey(CurrentSessionId);

        public static bool HasUser => List.ContainsValue(CurrentUserName);


        public static void Login()
        {
            var token = Authentication.GetToken(CurrentUserName);
            HttpContext.Current.Session[HttpContext.Current.Session.SessionID] = token;
            if (HasUser)
            {
                var previousUserSessionKey = List.First(d => d.Value == CurrentUserName).Key;
                List[previousUserSessionKey] = "OffLine";
            }
            if (!HasKey)
            {
                List.Add(CurrentSessionId, CurrentUserName);
            }
        }

        public static void CheckIsOnline()
        {
            if (!IsOnline)
            {
                Logout();
            }
        }

        public static void Logout()
        {
            HttpContext.Current.Session[CurrentSessionId] = null;
            List.Remove(CurrentSessionId);
        }

    }