Provider hosted App Error: You do not have permission...

Question

Hi everyone,
i'm using SharePoint online. I opened a provider hosted app and when I run this I get this error:
"Access denied. You do not have permission to perform this action or access this resource."
when I did debug I notice that it fall in this line:
webRequestEventArgs.WebRequestExecutor.RequestHeaders["Authorization"]
and "webRequestEventArgs.WebRequestExecutor.RequestHeaders"
is empty.
what can I do?
thank you!

Answer 1

i'm trying to add an item ti my list:
protected void Page_Load(object sender, EventArgs e)
//constant string SharePoint principal
string SharePointPrincipal = "00000003-0000-0ff1-ce00-000000000000";
var contextToken = TokenHelper.GetContextTokenFromRequest(Page.Request);
Uri hostWeb = new Uri(Page.Request["SPHostUrl"]);
string realm = TokenHelper.GetRealmFromTargetUrl(hostWeb);
string appOnlyAccessToken = TokenHelper.GetAppOnlyAccessToken(SharePointPrincipal, hostWeb.Authority, realm).AccessToken;
using (ClientContext clientContext = TokenHelper.GetClientContextWithAccessToken(hostWeb.ToString(), appOnlyAccessToken))
if (clientContext != null)
//ShariqTest is a custom List in my SharePoint site
var myList = clientContext.Web.Lists.GetByTitle("ListName");
ListItemCreationInformation listItemCreate = new ListItemCreationInformation();
Microsoft.SharePoint.Client.ListItem newItem = myList.AddItem(listItemCreate);
newItem["ColumnName"] = "Testing ";
newItem.Update();
clientContext.ExecuteQuery();
 "[and the  webRequestEventArgs.WebRequestExecutor.RequestHeaders["Authorization
is in TokenHelper.cs.
what do you think my problem is?