c# - Authentication request returned unexpected result: 404 -

exception details: google.gdata.client.gdatarequestexception: execution of authentication request returned unexpected result: 404

here code:

protected void button1_click(object sender, eventargs e) {     dataset ds = new dataset();     ds.tables.add("gmailcontacts");     ds.tables[0].columns.add("emailid");      requestsettings rs = new requestsettings("gmail", txtusername.value, txtpassword.value);     rs.autopaging = true;     contactsrequest cr = new contactsrequest(rs);      feed<contact> feed = cr.getcontacts();      foreach (contact contact in feed.entries)     {         foreach (email email in contact.emails)         {             datarow dr = ds.tables[0].newrow();             dr["emailid"] = email.address.tostring();             ds.tables[0].rows.add(dr);         }     }     gridview1.datasource = ds;     gridview1.databind(); } 

check own solution

steps:

1. go https://console.developers.google.com/project , create project.
2. select project, select apis & auth top left corner menu.
3. select credentials
4. create oauth button create new client id (application type - installed aplication.
5. fill field product name
6. save

after got client id native application with: client id, client secret, redirect uris

install google.apis.auth nuget

code

string clientid = null; // https://console.developers.google.com/project/xxx string clientsecret = null; // https://console.developers.google.com/project/xxx string accesscode = null; // code after getaccesstoken method string redirecturi = null; // https://console.developers.google.com/project/xxx string applicationname = null; // https://console.developers.google.com/project/xxx // scopes https://support.google.com/a/answer/162106?hl=en string scopes = null; // put scope https://www.google.com/m8/feeds/ string accesstype = "offline"; string tokentype = "refresh";  oauth2parameters parameters = new oauth2parameters {     clientid = clientid,     clientsecret = clientsecret,     redirecturi = redirecturi,     scope = scopes,     accesstype = accesstype,     tokentype = tokentype };  if (accesscode == null) {     string url = oauthutil.createoauth2authorizationurl(parameters);     // start webbrowser     process.start(url);      // load code web via popup, etc.     parameters.accesscode = accesscodefromweb; }  // check accesstoken , refreshtoken // after first acceess  getaccesstoken information if (accesstoken == null || refreshtoken == null) {     oauthutil.getaccesstoken(parameters);      // save yours accesstoken , refreshtoken next connection     accesstoken = parameters.accesstoken;     refreshtoken = parameters.refreshtoken; } else {        // restore token config file, etc.     parameters.accesstoken = accesstoken;     parameters.refreshtoken = refreshtoken; }  requestsettings rs = new requestsettings(applicationname, parameters);  return new contactsrequest(rs);