code: func auth(ctx *importer.SetupContext) (*oauth2.Config, error) {
  	clientID, secret, err := ctx.Credentials()
  	if err != nil {
  		return nil, err
  	}
  	return &oauth2.Config{
  		ClientID:     clientID,
  		ClientSecret: secret,
  		Endpoint: oauth2.Endpoint{
  			AuthURL:  authURL,
  			TokenURL: tokenURL,
  		},
  		RedirectURL: ctx.CallbackURL(),
  		// No scope needed for foursquare as far as I can tell
  	}, nil
  }
docs: // auth returns a new oauth2 Config