Google OAuth2: Required parameter is missing: grant_type

Question

I have tried just about everything, read every StackOverflow post on this issue but I still can't get it to work. Interestingly enough, I am able to get 200 OK response when sending a POST request via DHC REST API Client (Google Chrome app).

  var url = 'https://accounts.google.com/o/oauth2/token';
  var params = querystring.stringify({
    grant_type: 'authorization_code',
    code: req.body.code,
    client_id: req.body.clientId,
    client_secret: 'HIDDEN',
    redirect_uri: req.body.redirectUri
  });
  params = querystring.unescape(params); // doesn't work with or without string escaping

  request.post(url + '?' + params, function(error, response, body) {
    console.log(body);
  });

Answer 1

As @BenFortune has already mentioned, I was sending GET parameters as a POST request. It's amazing such a trivial thing has gone unnoticed after trying to figure it out for over an hour.

Now, I blame inconsistencies across OAuth providers for this. In the same application I am doing a GET request to Facebook to obtain access_token: https://graph.facebook.com/oauth/access_token. But Google expects a POST request to obtain access_token: https://accounts.google.com/o/oauth2/token

Correct version:

  var url = 'https://accounts.google.com/o/oauth2/token';
  var payload = {
    grant_type: 'authorization_code',
    code: req.body.code,
    client_id: req.body.clientId,
    client_secret: 'HIDDEN',
    redirect_uri: req.body.redirectUri
  };

  request.post(url, { form: payload }, function(error, response, body) {
    console.log(body);
  });