/// <summary> 
        /// This method will return a ClientContext object with the authentication cookie set. 
        /// The ClientContext should be disposed of as any other IDisposable 
        /// </summary> 
        /// <param name="targetSiteUrl"></param> 
        /// <returns></returns> 
        public static SharePointLists.Lists GetAuthenticatedContext(string targetSiteUrl, int popUpWidth, int popUpHeight)
        {
            CookieCollection cookies = null;
                cookies = ClaimClientContext.GetAuthenticatedCookies(targetSiteUrl, popUpWidth, popUpHeight);
                if (cookies == null) return null;

                SharePointLists.Lists contexto = new SharePointLists.Lists();

                try
                {
                    contexto.CookieContainer = new CookieContainer();
                    foreach (Cookie cookie in cookies)
                    {
                        contexto.CookieContainer.Add(cookie);
                    }
                }
                catch
                {
                    if (contexto != null) contexto.Dispose();
                    throw;
                }

                return contexto;
        }
 public RepositorioTarefas()
 {
     Contexto = ClaimClientContext.GetAuthenticatedContext(Constants.ENDRECO_SITE);
     Contexto.Url = Constants.ENDRECO_SITE + "/_vti_bin/Lists.asmx";
 }