How to generate access token using refresh token through Google Drive SDK in .NET?

Question

I have a .NET application that is using Google Drive to access the user's file. I am able to get the authorization code, and I have been able to exchange the authorization code by the AccessToken and the RefreshToken. The issue is that I cannot refresh the access token, and it expires after an hour.

Similar to this question: How to generate access token using refresh token through google drive API? except that I am working in .NET (using the Google.APIs... DLLs).

I am aware of this: https://developers.google.com/accounts/docs/OAuth2InstalledApp#refresh however, I am expecting some sort of method available in the IAuthorizationState or OAuth2Authenticator object to allow me refresh the access token.

Please advise. Thanks.

Please note that using this code I am able to get the Access Token. It is just that I am expecting this code to be inside the Google API.

    public class OAuth2AccessTokenReponse
    {
        public string access_token;
        public int expires_in;
        public string token_type; 
    }
    public static string refreshAccessToken()
    {
        using (System.Net.WebClient client = new System.Net.WebClient())
        {
            byte[] response = client.UploadValues("https://accounts.google.com/o/oauth2/token", new System.Collections.Specialized.NameValueCollection(){
                {"client_id", ClientID},
                {"client_secret", ClientSecret},
                {"refresh_token", "XXXXX"},
                {"grant_type", "refresh_token"}
            });
            string sresponse = System.Text.Encoding.Default.GetString(response);
            OAuth2AccessTokenReponse o = (OAuth2AccessTokenReponse) Newtonsoft.Json.JsonConvert.DeserializeObject(sresponse, typeof(OAuth2AccessTokenReponse));
            return o.access_token;        
        }
    }

Answer 1

I studied a more suitable sample: the Tasks.WinForms.NoteMgr of the GoogleApisSample... and with it I found the solution.

The solution is in the code below. The key part of it is calling arg.RefreshToken(state);

Thanks.

    public static Authentication.IAuthenticator UseSavedAuthorization()
    {          

        var provider = new NativeApplicationClient(GoogleAuthenticationServer.Description);
        provider.ClientIdentifier = ClientID;
        provider.ClientSecret = ClientSecret;

        OAuth2Authenticator<NativeApplicationClient> auth = new OAuth2Authenticator<NativeApplicationClient>(provider, getState);

        auth.LoadAccessToken();

        return auth;             
    }


public static IAuthorizationState getState(NativeApplicationClient arg)
    {
        IAuthorizationState state = new AuthorizationState(new[] { TasksService.Scopes.Tasks.GetStringValue(), 
                DriveService.Scopes.DriveFile.GetStringValue() , DriveService.Scopes.Drive.GetStringValue()
        });
        state.Callback = new Uri(NativeApplicationClient.OutOfBandCallbackUrl);

        state.RefreshToken = "<refresh token previously saved>";        
        arg.RefreshToken(state); 

        return state; 
    }`