Unable to get access token from Google OAuth2 Token endpoint

Question

I'm trying to retrieve an access token from Google's authorization endpoint, however I keep getting 401: Unauthorized.

I'm pretty sure all the values being sent (authorization code, client's id, client's secret, redirect uri and grant type) are correct.

My code is the following:

using (HttpClient client = new HttpClient()) {
    IEnumerable<KeyValuePair<string,string>> data = new List<KeyValuePair<string,string>> 
    {
          new KeyValuePair<string,string>("code", "CODE_HERE"),
          new KeyValuePair<string,string>("client_id", "CLIENT_ID_HERE"),
          new KeyValuePair<string,string>("client_secret", "CLIENT_SECRET_HERE"),
          new KeyValuePair<string,string>("redirect_uri", "REDIRECT_URI_HERE"),
          new KeyValuePair<string,string>("grant_type", "authorization_code"),
    }

    HttpContent content = new FormUrlEncodedContent(data);

    /* I'm getting 401 Unauthorized */
    HttpResponseMessage response = await client.PostAsync("https://www.googleapis.com/oauth2/v3/token", content);
}

The response's JSON is:

{
    "error": "invalid_client",
    "error_description": "Unauthorized"
}

However, I'm copying & pasting the client's id and client's secret from my Google Developer control panel, so there is no way they are wrong.

Any help?

Do you still get the error when you pass your credentials into the OAuth2.0 Playground? https://developers.google.com/oauthplayground/ — Andy, Dec 13 '14 at 00:00
@vtortola I'm very sorry. This project got discontinued before I managed to find a solution. If you guys happen to find it, post it here as I'm still very interested in learning! — Matias Cicero, Apr 10 '15 at 02:16
I hope this helps: http://stackoverflow.com/questions/28548920/googles-openidconnect-return-a-base64-token-that-cannot-be-parsed — vtortola, Apr 10 '15 at 13:27

score 0 · Answer 1 · answered Feb 01 '19 at 15:42

Here is what worked for me. In this sample, I'm using the RefreshToken to get an AccessToken.

var client_id = ConfigurationManager.AppSettings.Get("GoogleClientId");
                var client_secret = ConfigurationManager.AppSettings.Get("GoogleSecret");
                var grant_type = "refresh_token";

                var url = "https://www.googleapis.com/oauth2/v4/token";

                IEnumerable<KeyValuePair<string, string>> data = new List<KeyValuePair<string, string>>
                {
                    new KeyValuePair<string,string>("client_id", client_id),
                    new KeyValuePair<string,string>("client_secret", client_secret),
                    new KeyValuePair<string,string>("grant_type", grant_type),
                    new KeyValuePair<string,string>("refresh_token", refreshToken),
                };

                var client = new HttpClient();
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/x-www-form-urlencoded"));

                HttpContent contentPost = new FormUrlEncodedContent(data);

                HttpResponseMessage response = await client.PostAsync(url, contentPost);
                var result = response.Content.ReadAsStringAsync().Result;
                return JsonConvert.DeserializeObject<GoogleAPIAuth>(result);

Here is my GoogleAPIAuth class.

public class GoogleAPIAuth
    {
        public string client_secret { get; set; }
        public string grant_type { get; set; }
        public string refresh_token { get; set; }
        public string client_id { get; set; }
        public string access_token { get; set; }
        public string expires_in { get; set; }
        public string token_type { get; set; }
    }

Unable to get access token from Google OAuth2 Token endpoint

1 Answers1