RESTCall.cs

using (var client = new HttpClient())
{
    //Enable signon and read users' profile
    using (var request = new HttpRequestMessage(HttpMethod.Get, "https://graph.microsoft.com/beta/me"))
    {
        request.Headers.Add("Authorization", "Bearer " + token);
        request.Headers.Add("Accept", "application/json;odata.metadata=minimal");

        using (var response = client.SendAsync(request).Result)
        {

            if (response.StatusCode == HttpStatusCode.OK)
            {
                var json = JObject.Parse(response.Content.ReadAsStringAsync().Result);

                ViewBag.CurrentUserDisplayName = json["displayName"].ToString();

            }

        }
    }
}