Unable to authenticate as admin

Are you using a self-signed certificate? If yes - this is probably the problem. You can try editing the ApplicationAuthenticationStateProvider.cs file and change this code:

            catch (HttpRequestException ex)
            {
            }

to this

            catch (HttpRequestException ex)
            {
                throw ex;
            }

This will throw an exception and it should appear in the logs (if enabled) or in the Event Log (in Application).