class LoginData : INotifyPropertyChanged
    {
        private string username, password;

        public LoginData() { }

        public LoginData(string username, string password)
        {
            Username = username;
            Password = password;
        }

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public static async Task<bool> Login(LoginData logindata)
        {
            string json = JsonConvert.SerializeObject(logindata);
            var content = new StringContent(json, Encoding.UTF8, "application/json");
            HttpResponseMessage response = client.PostAsync(myRest + "/login" ,content).Result;
            if (response.IsSuccessStatusCode)
            {
                string result = await response.Content.ReadAsStringAsync();
                if (String.Compare(result, "OK") == 0)
                    return true;
            }
            return false;
        }