TrelloIndexController.cs

public class TrelloController : Controller
{
    //...continuação

    public async Task<IActionResult> Index()
    {
        var model = await TrelloGetRequest<TrelloUser>("members/me?boards=all&organizations=all&");

        return View("Index", model);
    }

    private async Task<T> TrelloGetRequest<T>(string url)
    {
        var request = await _httpClient.GetAsync($"{url}key={_apiKey}&token={_token}");

        if (!request.IsSuccessStatusCode)
            throw new Exception("Deu errado...");

        var model = await request.Content.ReadAsAsync<T>();

        return model;
    }
}