// GET api/values/5
 public async Task<string> Get(string id)
 {
    string contentUrl = $"https://graph.microsoft.com/v1.0/me/drive/items/{id}/content";
    using (var client = new HttpClient())
    {
       var retval = await client.GetAsStringOnBehalfOfScriptUser(contentUrl);
       return retval;
    }
 }