OAuth with Google data API for .NET returning HTTP 400: Bad Request

I struggled through this and was able to put together my own MVC2 class to handle this whole process. Take a look and let me know if this helps you out.

public class GoogleController : ApplicationController
{
    //
    // GET: /Google/

    public ActionResult Index()
    {
        return View();
    }

    public ActionResult Authorize()
    {
        OAuthParameters parameters = BuildParameters();

        // build the token for unauthorized requests and generate the url
        GetUnauthorizedRequestToken(parameters);
        string authorizationUrl = OAuthUtil.CreateUserAuthorizationUrl(parameters);

        // store the parameters temporarily and redirect to google for authorization
        SaveParametersTokens(parameters);
        Response.Redirect(authorizationUrl);
        return View();
    }

    public ActionResult Oauth()
    {
        // retrieve and update the tokens for temporary authentication
        OAuthParameters parameters = BuildParameters();
        OAuthUtil.UpdateOAuthParametersFromCallback(Request.Url.Query, parameters);

        // finally, get the token we need b@#$!!!
        OAuthUtil.GetAccessToken(parameters);

        // save those tokens into the database
        SaveParametersTokens(parameters);

        // all the success in the world, return back
        return RedirectToAction("Index", "Admin");
    }

    public ActionResult DeleteParametersTokens()
    {
        var oldTokens = (from t in context.GO_GoogleAuthorizeTokens select t);

        // if there is a token, call google to remove it
        /*if (oldTokens.Count() > 0)
        {
            GO_GoogleAuthorizeToken tokens = oldTokens.First();
            AuthSubUtil.revokeToken(tokens.Token, null);
        }*/

        // delete the tokens from the database
        context.GO_GoogleAuthorizeTokens.DeleteAllOnSubmit(oldTokens);
        context.SubmitChanges();

        // redirect to the administrator homepage when the tokens are deleted
        return RedirectToAction("Index", "Admin");
    }

    #region private helper methods

    private void GetUnauthorizedRequestToken(OAuthParameters parameters)
    {
        String requestTokenUrl = "https://www.google.com/accounts/OAuthGetRequestToken";
        Uri requestUri = new Uri(string.Format("{0}?scope={1}", requestTokenUrl, OAuthBase.EncodingPerRFC3986(parameters.Scope)));

        // callback is only needed when getting the request token
        bool callbackExists = false;
        if (!string.IsNullOrEmpty(parameters.Callback))
        {
            parameters.BaseProperties.Add(OAuthBase.OAuthCallbackKey, parameters.Callback);
            callbackExists = true;
        }

        string headers = OAuthUtil.GenerateHeader(requestUri, "GET", parameters);
        System.Net.WebRequest request = System.Net.WebRequest.Create(requestUri);
        request.Headers.Add(headers);

        System.Net.WebResponse response = request.GetResponse();
        string result = "";
        if (response != null)
        {
            System.IO.Stream responseStream = response.GetResponseStream();
            System.IO.StreamReader reader = new System.IO.StreamReader(responseStream);
            result = reader.ReadToEnd();
        }

        if (callbackExists)
        {
            parameters.BaseProperties.Remove(OAuthBase.OAuthCallbackKey);
        }

        // split results and update parameters
        SortedDictionary<string, string> responseValues = OAuthBase.GetQueryParameters(result);
        parameters.Token = responseValues[OAuthBase.OAuthTokenKey];
        parameters.TokenSecret = responseValues[OAuthBase.OAuthTokenSecretKey];
    }

    private bool SaveParametersTokens(OAuthParameters parameters)
    {
        try
        {
            // first delete any old ones
            var oldTokens = (from t in context.GO_GoogleAuthorizeTokens select t);
            context.GO_GoogleAuthorizeTokens.DeleteAllOnSubmit(oldTokens);
            context.SubmitChanges();

            // now create a new one
            GO_GoogleAuthorizeToken newToken = new GO_GoogleAuthorizeToken
            {
                Token = parameters.Token,
                TokenSecret = parameters.TokenSecret
            };
            context.GO_GoogleAuthorizeTokens.InsertOnSubmit(newToken);
            context.SubmitChanges();
        }
        catch { return false; }

        return true;
    }

    private OAuthParameters BuildParameters()
    {
        // build the base parameters
        string scope = "https://www.google.com/calendar/feeds/ https://docs.google.com/feeds/ https://mail.google.com/mail/feed/atom/";
        string callback = String.Format("http://{0}/Google/Oauth", Request.Url.Authority);
        OAuthParameters parameters = new OAuthParameters
        {
            ConsumerKey = kConsumerKey,
            ConsumerSecret = kConsumerSecret,
            Scope = scope,
            Callback = callback,
            SignatureMethod = "HMAC-SHA1"
        };

        // check to see if we have saved tokens
        var tokens = (from a in context.GO_GoogleAuthorizeTokens select a);
        if (tokens.Count() > 0)
        {
            GO_GoogleAuthorizeToken token = tokens.First();
            parameters.Token = token.Token;
            parameters.TokenSecret = token.TokenSecret;
        }

        return parameters;
    }

    #endregion
}