OAuthAuthorizationServerHandler SendErrorPageAsync

internal class OAuthAuthorizationServerHandler : AuthenticationHandler<OAuthAuthorizationServerOptions>
{
  private Task SendErrorAsJsonAsync(
      BaseValidatingContext<OAuthAuthorizationServerOptions> validatingContext)
  {
      string error = validatingContext.HasError ? validatingContext.Error : Constants.Errors.InvalidRequest;
      string errorDescription = validatingContext.HasError ? validatingContext.ErrorDescription : null;
      string errorUri = validatingContext.HasError ? validatingContext.ErrorUri : null;

      var memory = new MemoryStream();
      byte[] body;
      using (var writer = new JsonTextWriter(new StreamWriter(memory)))
      {
          writer.WriteStartObject();
          writer.WritePropertyName(Constants.Parameters.Error);
          writer.WriteValue(error);
          if (!string.IsNullOrEmpty(errorDescription))
          {
              writer.WritePropertyName(Constants.Parameters.ErrorDescription);
              writer.WriteValue(errorDescription);
          }
          if (!string.IsNullOrEmpty(errorUri))
          {
              writer.WritePropertyName(Constants.Parameters.ErrorUri);
              writer.WriteValue(errorUri);
          }
          writer.WriteEndObject();
          writer.Flush();
          body = memory.ToArray();
      }
      Response.StatusCode = 400;
      Response.ContentType = "application/json;charset=UTF-8";
      Response.Headers.Set("Cache-Control", "no-cache");
      Response.Headers.Set("Pragma", "no-cache");
      Response.Headers.Set("Expires", "-1");
      Response.Headers.Set("Content-Length", body.Length.ToString(CultureInfo.InvariantCulture));
      return Response.WriteAsync(body, Request.CallCancelled);
  }
}