how to send response to model after autheticate using passport and backbone.js

To authenticate,i have sent post request to server from backbone.js like this

model.save({"email":"sil@gmail.com","password":"silvester"}, {
   successs:function(model,res){

   },
   error:function(){

   }
});

i have received in server side like this

app.post('/login', passport.authenticate('local', {
    successRedirect: '/mainpage',
    failureRedirect: '/login'
}));

in above coding if authentication success i redirect to mainpage and then i have tried to show another one html page like this

app.get('/mainpage',function(req,res) {
    console.log("mainpage");
    res.sendfile('/mainpage.html');
});

after redirect that mainpage i got that console result but i could not redirect to another webpage. how to work it out and then is there anyway to send response only for that post request(above mentioned post request).if i send response to that post request i can easily receive that response within success function and then i can proceed my work but in passport there is only redirect option so it is going to another get request ,from this how can i sent response to frontend ? and where can i receive ?.so how to send response without redirect and how to solve this one.anyone solve this. thank you

model.save will make an ajax request to your server.

I think when you do res.sendfile('/mainpage.html');, it returns the html page in ajax response. Can you check in Developer Console in the browser?

you should check that if the request is ajax then return a 401 http status code and do the redirection on the client side using window.location="/mainpage.html"

it may help you to respond to same post request

app.post('/login', passport.authenticate('local', { failureRedirect: '/login' }), function(req, res) { res.redirect('/mainpage'); });