Google+ API: How can I use RefreshTokens to avoid requesting access every time my app launches?

Question

I\'m trying to use the Google+ API to access info for the authenticated user. I\'ve copied some code from one of the samples, which works fine (below), however I\'m having t

Answer 1

I also had problems with getting "offline" authentication to work (i.e. acquiring authentication with a refresh token), and got HTTP-response 400 Bad request with a code similar to the OP's code. However, I got it to work with the line client.ClientCredentialApplicator = ClientCredentialApplicator.PostParameter(this.clientSecret); in the Authenticate-method. This is essential to get a working code -- I think this line forces the clientSecret to be sent as a POST-parameter to the server (instead of as a HTTP Basic Auth-parameter).

This solution assumes that you've already got a client ID, a client secret and a refresh-token. Note that you don't need to enter an access-token in the code. (A short-lived access-code is acquired "under the hood" from the Google server when sending the long-lived refresh-token with the line client.RefreshAuthorization(state);. This access-token is stored as part of the auth-variable, from where it is used to authorize the API-calls "under the hood".)

A code example that works for me with Google API v3 for accessing my Google Calendar:

class SomeClass
{

    private string clientID         = "XXXXXXXXX.apps.googleusercontent.com";
    private string clientSecret     = "MY_CLIENT_SECRET";
    private string refreshToken     = "MY_REFRESH_TOKEN";
    private string primaryCal       = "MY_GMAIL_ADDRESS";

    private void button2_Click_1(object sender, EventArgs e)
    {
        try
        {
            NativeApplicationClient client = new NativeApplicationClient(GoogleAuthenticationServer.Description, this.clientID, this.clientSecret);
            OAuth2Authenticator auth = new OAuth2Authenticator(client, Authenticate);

            // Authenticated and ready for API calls...

            // EITHER Calendar API calls (tested):
            CalendarService cal = new CalendarService(auth);
            EventsResource.ListRequest listrequest = cal.Events.List(this.primaryCal);
            Google.Apis.Calendar.v3.Data.Events events = listrequest.Fetch();
            // iterate the events and show them here.

            // OR Plus API calls (not tested) - copied from OP's code:
            var plus = new PlusService(auth);
            plus.Key = "BLAH";  // don't know what this line does.
            var me = plus.People.Get("me").Fetch();
            Console.WriteLine(me.DisplayName);

            // OR some other API calls...
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error while communicating with Google servers. Try again(?). The error was:\r\n" + ex.Message + "\r\n\r\nInner exception:\r\n" + ex.InnerException.Message);
        }
    }

    private IAuthorizationState Authenticate(NativeApplicationClient client)
    {
        IAuthorizationState state = new AuthorizationState(new string[] { }) { RefreshToken = this.refreshToken };

        // IMPORTANT - does not work without:
        client.ClientCredentialApplicator = ClientCredentialApplicator.PostParameter(this.clientSecret);

        client.RefreshAuthorization(state);
        return state;
    }
}