GraphHelper.cs

 public class GraphHelper
  {
      private static GraphServiceClient graphClient;
      public static void Initialize(IAuthenticationProvider authProvider)
      {
          graphClient = new GraphServiceClient(authProvider);
      }

      public static async Task<IEnumerable<User>> GetUsersAsync()
      {
          // GET /users
          return await graphClient.Users.Request().GetAsync();
      }
  }