Why am I not receiving a RefreshToken from a Google OAuth request? - asp.net-mvc

Question

I am attempting to integrate Google Calendar into my application and I am having some problems with the OAuth authorization passing off a RefreshToken. I receive an AccessToken with no issue, but the RefreshToken property is null. See the line marked "ERROR HERE:" for where I am having the issue
My Asp.Net MVC controller (named OAuthController) looks like the following:
public ActionResult Index()
{
var client = CreateClient();
client.RequestUserAuthorization(new[] { "https://www.googleapis.com/auth/calendar" }, new Uri("http://localhost/FL.Evaluation.Web/OAuth/CallBack"));
return View();
}
public ActionResult CallBack()
{
if (string.IsNullOrEmpty(Request.QueryString["code"])) return null;
var client = CreateClient();
// Now getting a 400 Bad Request here
var state = client.ProcessUserAuthorization();
// ERROR HERE: The RefreshToken is NULL
HttpContext.Session["REFRESH_TOKEN"] = Convert.ToBase64String(Encoding.Unicode.GetBytes(state.RefreshToken));
return JavaScript("Completed!");
}
private static WebServerClient CreateClient()
{
return
new WebServerClient(
new AuthorizationServerDescription()
{
TokenEndpoint = new Uri("https://accounts.google.com/o/oauth2/token"),
AuthorizationEndpoint = new Uri("https://accounts.google.com/o/oauth2/auth"),
ProtocolVersion = ProtocolVersion.V20
}
, _GoogleClientId, _GoogleSecret);
}
I see in Google's API documents, that I need to ensure that the access_type requested is set to offline for a RefreshToken to be sent. How do I set this value in my Authenticator request?

Answer 1

After hours of fiddling with DotNetOpenAuth and the Google APIs published for .Net, I got nowhere fast. I decided to circumvent the libraries and went directly at the Google REST API with native HttpRequest and HttpResponse objects. My sanitized code for my MVC controller follows:
private static string _GoogleClientId = "CLIENT_ID";
private static string _GoogleSecret = "SECRET";
private static string _ReturnUrl = "http://localhost/OAuth/CallBack";
public ActionResult Index()
{
return Redirect(GenerateGoogleOAuthUrl());
}
private string GenerateGoogleOAuthUrl()
{
//NOTE: Key piece here, from Andrew's reply -> access_type=offline forces a refresh token to be issued
string Url = "https://accounts.google.com/o/oauth2/auth?scope={0}&redirect_uri={1}&response_type={2}&client_id={3}&state={4}&access_type=offline&approval_prompt=force";
string scope = UrlEncodeForGoogle("https://www.googleapis.com/auth/calendar https://www.googleapis.com/auth/calendar.readonly").Replace("%20", "+");
string redirect_uri_encode = UrlEncodeForGoogle(_ReturnUrl);
string response_type = "code";
string state = "";
return string.Format(Url, scope, redirect_uri_encode, response_type, _GoogleClientId, state);
}
private static string UrlEncodeForGoogle(string url)
{
string UnReservedChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_.~";
var result = new StringBuilder();
foreach (char symbol in url)
{
if (UnReservedChars.IndexOf(symbol) != -1)
{
result.Append(symbol);
}
else
{
result.Append('%' + String.Format("{0:X2}", (int)symbol));
}
}
return result.ToString();
}
class GoogleTokenData
{
public string Access_Token { get; set; }
public string Refresh_Token { get; set; }
public string Expires_In { get; set; }
public string Token_Type { get; set; }
}
public ActionResult CallBack(string code, bool? remove)
{
if (remove.HasValue && remove.Value)
{
Session["GoogleAPIToken"] = null;
return HttpNotFound();
}
if (string.IsNullOrEmpty(code)) return Content("Missing code");
string Url = "https://accounts.google.com/o/oauth2/token";
string grant_type = "authorization_code";
string redirect_uri_encode = UrlEncodeForGoogle(_ReturnUrl);
string data = "code={0}&client_id={1}&client_secret={2}&redirect_uri={3}&grant_type={4}";
HttpWebRequest request = HttpWebRequest.Create(Url) as HttpWebRequest;
string result = null;
request.Method = "POST";
request.KeepAlive = true;
request.ContentType = "application/x-www-form-urlencoded";
string param = string.Format(data, code, _GoogleClientId, _GoogleSecret, redirect_uri_encode, grant_type);
var bs = Encoding.UTF8.GetBytes(param);
using (Stream reqStream = request.GetRequestStream())
{
reqStream.Write(bs, 0, bs.Length);
}
using (WebResponse response = request.GetResponse())
{
var sr = new StreamReader(response.GetResponseStream());
result = sr.ReadToEnd();
sr.Close();
}
var jsonSerializer = new JavaScriptSerializer();
var tokenData = jsonSerializer.Deserialize<GoogleTokenData>(result);
Session["GoogleAPIToken"] = tokenData.Access_Token;
return JavaScript("Refresh Token: " + tokenData.Refresh_Token);
}
Big thanks to Kelp for a bit of the code in this snippet.

Answer 2

Adjust GoogleAuthenticationServer.Description to have an authorization endpoint URI that includes ?access_type=offline in the query string.

Answer 3

Simply add
AccessType = "offline",
to GoogleOAuth2AuthenticationOptions() object.