How to renew the access token using the refresh token?

This question isn’t duplicate AT ALL. I hope this help others not spending days like I have spent.

After almost 4 days I have found out how to get a fresh access token in the google api using OWIN.

I’m going to post the solution, but first, I MUST say that what helped me to start getting a clue about my error was setting up the Debug Symbols for the Katana project. See this link:
http://www.symbolsource.org/Public/Home/VisualStudio

This image show how to configure Debug Symbols Servers.

And this one shows the Katana Debug Symbols being loaded.

After that, I found out that my problem was that Google API was returning 403: Forbidden

“Access Not Configured. Please use Google Developers Console to activate the API for your project”

Then, found on stack overflow this post:
“Access Not Configured. Please use Google Developers Console to activate the API for your project.”

more specifically this Answer: https://stackoverflow.com/a/24401189/833846

After that, I went to Google Developers Console and setup up Google+ API

And then, voillá! It worked.

Now, the code to get a fresh access token using the refresh token (I haven’t found any way to accomplish that using the OWIN API).

public static class TokenValidator
{
    /// <summary>
    /// Obtém um novo access token na API do google.
    /// </summary>
    /// <param name="clientId"></param>
    /// <param name="clientSecret"></param>
    /// <param name="refreshToken"></param>
    /// <returns></returns>
    public static GoogleRefreshTokenModel ValidateGoogleToken(string clientId, string clientSecret, string refreshToken)
    {
        const string url = "https://accounts.google.com/o/oauth2/token";

        var parameters = new List<KeyValuePair<string, string>>
        {
            new KeyValuePair<string, string>("client_id", clientId),
            new KeyValuePair<string, string>("client_secret", clientSecret),
            new KeyValuePair<string, string>("grant_type", "refresh_token"),
            new KeyValuePair<string, string>("refresh_token", refreshToken)
        };

        var content = GetContentAsync(url, "POST",  parameters);

        var token = JsonConvert.DeserializeObject<GoogleRefreshTokenModel>(content);

        return token;
    }

    private static string GetContentAsync(string url, 
        string method = "POST",
        IEnumerable<KeyValuePair<string, string>> parameters = null)
    {
        return method == "POST" ? PostAsync(url, parameters) : GetAsync(url, parameters);
    }

    private static string PostAsync(string url, IEnumerable<KeyValuePair<string, string>> parameters = null)
    {
        var uri = new Uri(url);

        var request = WebRequest.Create(uri) as HttpWebRequest;
        request.Method = "POST";
        request.KeepAlive = true;
        request.ContentType = "application/x-www-form-urlencoded";

        var postParameters = GetPostParameters(parameters);

        var bs = Encoding.UTF8.GetBytes(postParameters);
        using (var reqStream = request.GetRequestStream())
        {
            reqStream.Write(bs, 0, bs.Length);
        }

        using (var response = request.GetResponse())
        {
            var sr = new StreamReader(response.GetResponseStream());
            var jsonResponse = sr.ReadToEnd();
            sr.Close();

            return jsonResponse;
        }
    }

    private static string GetPostParameters(IEnumerable<KeyValuePair<string, string>> parameters = null)
    {
        var postParameters = string.Empty;
        foreach (var parameter in parameters)
        {
            postParameters += string.Format("&{0}={1}", parameter.Key,
                HttpUtility.HtmlEncode(parameter.Value));
        }
        postParameters = postParameters.Substring(1);

        return postParameters;
    }

    private static string GetAsync(string url, IEnumerable<KeyValuePair<string, string>> parameters = null)
    {
        url += "?" + GetQueryStringParameters(parameters);

        var forIdsWebRequest = WebRequest.Create(url);
        using (var response = (HttpWebResponse)forIdsWebRequest.GetResponse())
        {
            using (var data = response.GetResponseStream())
            using (var reader = new StreamReader(data))
            {
                var jsonResponse = reader.ReadToEnd();

                return jsonResponse;
            }
        }
    }

    private static string GetQueryStringParameters(IEnumerable<KeyValuePair<string, string>> parameters = null)
    {
        var queryStringParameters = string.Empty;
        foreach (var parameter in parameters)
        {
            queryStringParameters += string.Format("&{0}={1}", parameter.Key,
                HttpUtility.HtmlEncode(parameter.Value));
        }
        queryStringParameters = queryStringParameters.Substring(1);

        return queryStringParameters;
    }
}

IMPORTANT 1: To get a refresh token you must set the “access_type” to “offline” in the “ExecuteResult” method, this way:

properties.Dictionary["access_type"] = "offline";

IMPORTANT 2: Once you get your refresh token, you must store it and in some secure source. Google API won’t issue you a new refresh token, unless you set “approval_prompt” to “force” before you call the line (in the same method):

context.HttpContext.GetOwinContext().Authentication.Challenge(properties, LoginProvider);

I also recommend taking a look at:

Google API Offline Access

Google OAUTH 2.0 Playground

Google API Discovery Check