title: Google Oauth giving code redeemed error
body: <p>Hi i am working on a project where a user logs in via google account.(localhost)
  I have implemented the google signup.
  As soon as I log in from my account I am getting the below error. </p>
  
  <pre><code>TokenError: Code was already redeemed.
         at Strategy.OAuth2Strategy.parseErrorResponse (c:\Projects\Internship_rideshare\node_modules\passport-google-oauth\node_modules\passport-oauth\node_modules\passport-oauth2\lib\strategy.js:298:12)
         at Strategy.OAuth2Strategy._createOAuthError (c:\Projects\Internship_rideshare\node_modules\passport-google-oauth\node_modules\passport-oauth\node_modules\passport-oauth2\lib\strategy.js:345:16)
         at c:\Projects\Internship_rideshare\node_modules\passport-google-oauth\node_modules\passport-oauth\node_modules\passport-oauth2\lib\strategy.js:171:43
         at c:\Projects\Internship_rideshare\node_modules\passport-google-oauth\node_modules\passport-oauth\node_modules\passport-oauth2\node_modules\oauth\lib\oauth2.js:176:18
         at passBackControl (c:\Projects\Internship_rideshare\node_modules\passport-google-oauth\node_modules\passport-oauth\node_modules\passport-oauth2\node_modules\oauth\lib\oauth2.js:123:9)
         at IncomingMessage.&lt;anonymous&gt; (c:\Projects\Internship_rideshare\node_modules\passport-google-oauth\node_modules\passport-oauth\node_modules\passport-oauth2\node_modules\oauth\lib\oauth2.js:142:7)
         at IncomingMessage.emit (events.js:129:20)
         at _stream_readable.js:908:16
         at process._tickCallback (node.js:355:11)
  </code></pre>
  
  <p>My code is as follows(snippet for google login):-</p>
  
  <pre><code>passport.use(new GoogleStrategy(google, function(req, accessToken, refreshToken, profile, done) {
    if (req.user) {
      User.findOne({ google: profile.id }, function(err, existingUser) {
        if (existingUser) {
          console.log('There is already a Google+ account that belongs to you. Sign in with that account or delete it, then link it with your current account.' );
          done(err);
        } else {
          User.findById(req.user.id, function(err, user) {
            user.google = profile.id;
            user.tokens.push({ kind: 'google', accessToken: accessToken });
            user.profile.displayName = user.profile.displayName || profile.displayName;
            user.profile.gender = user.profile.gender || profile._json.gender;
              //user.profile.picture = user.profile.picture || 'https://graph.facebook.com/' + profile.id + '/picture?type=large';
            user.save(function(err) {
              console.log('Google account has been linked.');
              done(err, user);
            });
          });
        }
      });
    } else {
      User.findOne({ google: profile.id }, function(err, existingUser) {
        if (existingUser) return done(null, existingUser);
        User.findOne({ email: profile._json.email }, function(err, existingEmailUser) {
          if (existingEmailUser) {
             console.log('There is already an account using this email address. Sign in to that account and link it with Google manually from Account Settings.' );
            done(err);
          } else {
            var user = new User();
            user.email = profile._json.email;
            user.google = profile.id;
            user.tokens.push({ kind: 'google', accessToken: accessToken });
            user.profile.displayName = profile.displayName;
            user.profile.gender = profile._json.gender;
              //user.profile.picture = 'https://graph.facebook.com/' + profile.id + '/picture?type=large';
            user.profile.location = (profile._json.location) ? profile._json.location.name : '';
            user.save(function(err) {
              done(err, user);
            });
          }
        });
      });
    }
  }));
  </code></pre>
  
  <p>I am stuck on it.Please help me out..thanks</p>