code: function loginCallback(req, res, test) {
    var state = JSON.parse(req.query.state);
    console.dir( state );
    var protocol = "https://";
    if(test === true || req.test) protocol = "http://";  //for testing
  
    var url = protocol + state.loginServer + "/services/oauth2/token";
  
    var options = {
      code: req.query.code,
      grant_type: 'authorization_code',
      client_id: process.env.SALESFORCE_CLIENT_ID,
      redirect_uri: process.env.SALESFORCE_REDIRECT_URL,
      client_secret: process.env.SALESFORCE_CLIENT_SECRET
    }
    
    request.post(url)
    .type("application/x-www-form-urlencoded")
    .send(options)
    .on("error", function(err){ return onError(res,err); })
    .end(function(sfRes){
      if(sfRes.error) return onError(res, sfRes.error);
      console.dir( sfRes.body )
      req.session.salesforce = JSON.stringify( sfRes.body );
      res.redirect(state.appUrl)
    })
  }
docs: Callback for the Salesforce Server Dance Auth Leg 2, adds the auth token to session