How to call REST api in provider hosted app

Question

I want to call the Site Design apis in my provider hosted app to install site designs. Site design apis are REST apis. But when I trying to call it is always giving me the 403 forbidden error. I am passing the request digest value as well. To test the REST query in provider hosted app I am just calling the lists from a site collection. But it is giving me 403 error. Below is my code, What I am doing wrong here?

string urlToRequest = clientContext.Web.Url + "/_api/web/lists";
HttpWebRequest endpointRequest = (HttpWebRequest)HttpWebRequest.Create(urlToRequest);
endpointRequest.Method = "GET";
FormDigestInfo formDigest = clientContext.GetFormDigestDirect();
endpointRequest.UseDefaultCredentials = true;
endpointRequest.Accept = "application/json; odata=verbose";
endpointRequest.ContentType = "application/json;odata=verbose";
endpointRequest.Headers.Add("X-RequestDigest", formDigest.DigestValue);
HttpWebResponse endpointResponse = (HttpWebResponse)endpointRequest.GetResponse();