code: func (factory *FacebookBeeFactory) OAuth2AccessToken(id, secret, code string) (*oauth2.Token, error) {
  	// Get facebook access token.
  	conf := &oauth2.Config{
  		ClientID:     id,
  		ClientSecret: secret,
  		RedirectURL:  api.CanonicalURL().String() + "/" + path.Join("oauth2", factory.ID(), id, secret),
  		Scopes:       []string{"public_profile", "publish_actions"},
  		Endpoint:     oauth2fb.Endpoint,
  	}
  	token, err := conf.Exchange(oauth2.NoContext, code)
  	if err != nil {
  		fmt.Println("Error:", err)
  		return nil, err
  	}
  
  	return token, nil
  }
docs: // OAuth2AccessToken returns the oauth2 access token.