SaveSession.cs

public static async Task SaveSessionAsync(string json)
        {
            try
            {
                File = Path.Combine(FileSystem.AppDataDirectory, "login.json");
                using (var file = new FileStream(File, FileMode.Create))
                using (var output = new StreamWriter(file, Encoding.UTF8))
                    await output.WriteAsync(json);
            }
            catch (System.Exception ex)
            {
                throw ex;
            }
        }