Google Calendar API - Bad Request (400) Trying To

Having got an authorisation code from Google for accessing a user's calendar, I'm now trying to swap this for an access token. According to their own docs:

The actual request might look like:

POST /o/oauth2/token HTTP/1.1
Host: accounts.google.com
Content-Type: application/x-www-form-urlencoded

code=4/v6xr77ewYqhvHSyW6UJ1w7jKwAzu&
client_id=8819981768.apps.googleusercontent.com&
client_secret={client_secret}&
redirect_uri=https://oauth2-login-demo.appspot.com/code&
grant_type=authorization_code

My attempt to access this is as follows (C#):

string url = "https://accounts.google.com/o/oauth2/token";
WebRequest request = HttpWebRequest.Create(url); 
request.Method = "POST"; 
request.ContentType = "application/x-www-form-urlencoded"; 

string body = "code=<the_code_I_received>&\r\n"
    + "client_id=<my_client_id>&\r\n"
    + "client_secret=<my_client_secret>&\r\n"
    + "redirect_uri=http://localhost:4300\r\n"
    + "grant_type=authorization_code&\r\n"
                            ;
byte[] bodyBytes = Encoding.ASCII.GetBytes(body); 
request.ContentLength = bodyBytes.Length ; 
Stream bodyStream = request.GetRequestStream(); 
bodyStream.Write(bodyBytes, 0, bodyBytes.Length); 
bodyStream.Close(); 

try 
{
    request.GetResponse();

'http://localhost:4300' is exactly the same as I put in the original request (and it was valid because I got the code back through listening as a web server on that port), but I also tried just 'http://localhost' just in case.

I tried a number of suggestions such as setting the proxy to null (no change) and changing Accept (wasn't allowed to add that header to the web request).

In each case I get the HTTP 400 - bad request back (the try / catch fires with an exception stating that).

Putting a trailing slash after /token (I'll try anything!) resulted in a 500 Internal Server Error, so that wasn't it either.

Any idea what I'm doing wrong?

Do you need the new lines \r\n in the body? This code works for me...

var req0 = WebRequest.Create("https://accounts.google.com/o/oauth2/token");
req0.Method = "POST";
string postData = string.Format("code={0}&client_id={1}&client_secret={2}&redirect_uri={3}&grant_type=authorization_code",
code, //the code i got back
"2xxx61.apps.googleusercontent.com", "XJxxxFy",
"http://localhost:1599/home/oauth2callback"); //my return URI

byte[] byteArray = Encoding.UTF8.GetBytes(postData);
req0.ContentType = "application/x-www-form-urlencoded";
req0.ContentLength = byteArray.Length;
using (Stream dataStream = req0.GetRequestStream())
{
    dataStream.Write(byteArray, 0, byteArray.Length);
    dataStream.Close();
}
try
{
using (WebResponse response = req0.GetResponse())
    {
    using (var dataStream = response.GetResponseStream())
        {    
        using (StreamReader reader = new StreamReader(dataStream))
        {
         string responseFromServer = reader.ReadToEnd();
         var ser = new JavaScriptSerializer();
            accessToken = ser.DeserializeObject(responseFromServer);
        }
    }
}
}
catch (WebException wex){ var x = wex; }
catch (Exception ex){var x = ex;}