Unauthorized error when trying to get Nest Access Token

Question

Everything was working fine until a couple days ago, I started getting an Unauthorized error when trying to get a Nest Access Token. I've double checked and the client ID and client secret code are all correct. Any ideas on what could be causing it?

HttpWebRequest request = WebRequest.CreateHttp("https://api.home.nest.com/oauth2/access_token?");
var token = await request.GetValueFromRequest<NestToken>(string.Format(
    "client_id={0}&code={1}&client_secret={2}&grant_type=authorization_code",
                CLIENTID,
                code.Value,
                CLIENTSECRET));

public async static Task<T> GetValueFromRequest<T>(this HttpWebRequest request, string postData = null)
{
    T returnValue = default(T);

    if (!string.IsNullOrEmpty(postData))
    {
        byte[] requestBytes = Encoding.UTF8.GetBytes(postData);

        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";

        using (var postStream = await request.GetRequestStreamAsync())
        {
            await postStream.WriteAsync(requestBytes, 0, requestBytes.Length);
        }
    }
    else
    {
        request.Method = "GET";
    }

    var response = await request.GetResponseAsync();

    if (response != null)
    {
        using (var receiveStream = response.GetResponseStream())
        {
            using (var reader = new StreamReader(receiveStream))
            {
                var json = await reader.ReadToEndAsync();
                    var serializer = new DataContractJsonSerializer(typeof(T));

                using (var tempStream = new MemoryStream(Encoding.UTF8.GetBytes(json)))
                {
                    return (T)serializer.ReadObject(tempStream);
                }
            }
        }
    }

    return returnValue;
}

Answer 1

This turned out to be because of a fault on Nest's end which was later fixed.

Answer 2

While I can't provide an answer I can confirm the same thing is happening to my iOS app in the same timeframe.

Taking my url and post values works fine using postman in chrome. Alamofire is throwing up error 401, as is native swift test code like yours.

Have Nest perhaps changed their https negotiation?