Default.aspx.cs

protected void Page_Load(object sender, EventArgs e)
{
    // The following code gets the client context and Title property by using TokenHelper.
    // To access other properties, the app may need to request permissions on the host web.
    var spContext = SharePointContextProvider.Current.GetSharePointContext(Context);

    using (var clientContext = spContext.CreateUserClientContextForSPHost())
    {
        clientContext.Load(clientContext.Web, web => web.Title);
        clientContext.ExecuteQuery();
        Response.Write(clientContext.Web.Title);
    }
}