DotNetOpenAuth Google API Offline Access

Question

I've spent some time over the last few days trying to implement a feature for my web application. The feature should add new events to a users google calendar while they are offline. I read the Google OAuth2 documentation for web server applications and seem to understand the basics of it. I created a link to authorize the application for offline access:

    <a target='_blank' href='https://accounts.google.com/o/oauth2/auth?scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Ftasks&response_type=code&client_id=<MY CLIENT ID>&access_type=offline&redirect_uri=http%3A%2F%2Flocalhost:49949%2Foauth2callback.aspx'>Grant Tasks Permission</a>

If the user accepts then I capture the refresh token at the redirect uri like this:

    private static OAuth2Authenticator<WebServerClient> _authenticator;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (HttpContext.Current.Request["code"] != null)
        {
            _authenticator = CreateAuthenticator();
            _authenticator.LoadAccessToken();
        }
        Response.Write("Refresh Token: " + _authenticator.State.RefreshToken);

    }

    private OAuth2Authenticator<WebServerClient> CreateAuthenticator()
    {
        var provider = new WebServerClient(GoogleAuthenticationServer.Description);
        provider.ClientIdentifier = "<MY CLIENT ID>";
        provider.ClientSecret = "<MY CLIENT SECRET>";
        return new OAuth2Authenticator<WebServerClient>(provider, GetAuthorization);
    }

    private IAuthorizationState GetAuthorization(WebServerClient client)
    {
        return client.ProcessUserAuthorization(new HttpRequestInfo(HttpContext.Current.Request));
    }

For testing purposes I have been copying the refresh token to a text file for further use.

My problem is using this refresh token for offine access. I have been using this code to refresh the token:

    protected void btnGetTasks_Click(object sender, EventArgs e)
    {
        if (_service == null)
        {
            _authenticator = CreateAuthenticator();
            _service = new TasksService(new BaseClientService.Initializer() { Authenticator = _authenticator });
        }

        var cl = _service.Tasklists.List().Fetch();
    }

    private OAuth2Authenticator<WebServerClient> CreateAuthenticator()
    {
        // Register the authenticator.
        var provider = new WebServerClient(GoogleAuthenticationServer.Description);
        provider.ClientIdentifier = "<MY CLIENT ID>";
        provider.ClientSecret = "<MY CLIENT SECRET>";
        var authenticator = new OAuth2Authenticator<WebServerClient>(provider, GetAuthorization);
        return authenticator;
    }

    private IAuthorizationState GetAuthorization(WebServerClient client)
    {                      
        string scope = "https://www.googleapis.com/auth/tasks";
        IAuthorizationState state = new AuthorizationState(new[] { scope });
        state.RefreshToken = "<REFRESH TOKEN FROM FIRST STEP>";
        var result = client.RefreshToken(state);
        return client.ProcessUserAuthorization();
    }

Everything seems fine at this point. When I step through the code I can see the result from client.RefreshToken(state) is true. The issue is when I call this line of code:

_service.Tasklists.List().Fetch();

It returns a (401) unauthorized error from google. I'm looking into the cause but I am not sure how to proceed and I am running short on time with this feature. Any advice would be greatly appreciated. Thanks!

score 0 · Answer 1 · answered May 15 '13 at 18:03

Seems just the act of putting code on here always helps me figure it out a little sooner :)

It now appears this line is unnecessary:

return client.ProcessUserAuthorization();

removing that from the GetAuthorization method and just returning the state passed to RefreshToken has resolved the unauthorized error. I'll leave the question in case it stumps anyone else.

DotNetOpenAuth Google API Offline Access

1 Answers1