Using Google experimental implementation of OAuth 2.0 to access existing API endpoints

I found the answer I was looking for. I had to convert PHP to MVC, but pretty easy:

http://codecri.me/case/430/get-a-users-google-email-address-via-oauth2-in-php/

My MVC Login sandbox code looks like the following. (using JSON.Net http://json.codeplex.com/)

public ActionResult Login()
    {
        string url = "https://accounts.google.com/o/oauth2/auth?";
        url += "client_id=<google-clientid>";
        url += "&redirect_uri=" +
          // Development Server :P 
          HttpUtility.UrlEncode("http://localhost:61857/Account/OAuthVerify");
        url += "&scope=";
        url += HttpUtility.UrlEncode("http://www.google.com/calendar/feeds/ ");
        url += HttpUtility.UrlEncode("http://www.google.com/m8/feeds/ ");
        url += HttpUtility.UrlEncode("http://docs.google.com/feeds/ ");
        url += HttpUtility.UrlEncode("https://mail.google.com/mail/feed/atom ");
        url += HttpUtility.UrlEncode("https://www.googleapis.com/auth/userinfo.email ");
        url += HttpUtility.UrlEncode("https://www.googleapis.com/auth/userinfo.profile ");
        url += "&response_type=code";

        return new RedirectResult(url);
    }

The code returned is proof of Authorization token from the user, which then needs to be turn into a Authentication (accessToken) to access resources. My MVC OAuthVerify then looks like:

    public ActionResult AgentVerify(string code)
    {
        JObject json;

        if (!string.IsNullOrWhiteSpace(code))
        {
            NameValueCollection postData = new NameValueCollection();
            postData.Add("code", code);
            postData.Add("client_id", "<google-clientid>");
            postData.Add("client_secret", "<google-client-secret>");
            postData.Add("redirect_uri", "http://localhost:61857/Account/OAuthVerify");
            postData.Add("grant_type", "authorization_code");

            try
            {   
                json = JObject.Parse(
                  HttpClient.PostUrl(
                    new Uri("https://accounts.google.com/o/oauth2/token"), postData));
                string accessToken = json["access_token"].ToString();
                string refreshToken = json["refresh_token"].ToString();
                bool isBearer = 
                  string.Compare(json["token_type"].ToString(), 
                                 "Bearer", 
                                 true, 
                                 CultureInfo.CurrentCulture) == 0;

                if (isBearer)
                {
                    json = JObject.Parse(
                      HttpClient.GetUrl(
                        new Uri("https://www.googleapis.com/oauth2/v1/userinfo?alt=json"),
                      accessToken));
                    string userEmail = json["email"].ToString();
                }
                return View("LoginGood"); 
            }
            catch (Exception ex)
            {
                ErrorSignal.FromCurrentContext().Raise(ex); //ELMAH
            }
        }
        return View("LoginBad");
    }

To complete how everything works, I've included the HttpClient utility I created in case anyone needed it.

public class HttpClient
{
    public static string GetUrl(Uri url, string OAuth)
    {
        string result = string.Empty;

        using (WebClient httpClient = new WebClient())
        {
            httpClient.Headers.Add("Authorization","OAuth " + OAuth);
            result = httpClient.DownloadString(url.AbsoluteUri);
        }

        return result;
    }

    public static string PostUrl(Uri url, NameValueCollection formData)
    {
        string result = string.Empty;

        using (WebClient httpClient = new WebClient())
        {
            byte[] bytes = httpClient.UploadValues(url.AbsoluteUri, "POST", formData);
            result = Encoding.UTF8.GetString(bytes);
        }

        return result;
    }
}

Again, this is test code just to get it to function, I do not recommend using this as-is in a production environment.