How to Facebook Connect on server side via Ajax using Node, Express and Connect-auth - ajax

Question

I've got a piece of code that look like this.
app.get('/auth/facebook', function( request, response ) {
if( request.session.user ){
response.render( 'index.jade' );
} else {
request.authenticate(['facebook'], function(error, authenticated) {
if( authenticated ) {
request.session.user = request.getAuthDetails().user;
response.writeHead(303, { 'Location': "/auth/facebook" });
}
});
}
});
If there is a user in session it will render the page, if not it will get a user from Facebook and store that in a session variable and reload the page... and render it. It works perfectly fine. But I want to trigger that piece of code via AJAX and do something like this:
app.get('/auth/facebook', function( request, response ) {
response.contentType('application/json');
if( request.session.user ){
response.send(JSON.stringify({'authenticated':true}));
} else {
request.authenticate(['facebook'], function(error, authenticated) {
if( authenticated ) {
request.session.user = request.getAuthDetails().user;
response.writeHead(303, { 'Location': "/auth/facebook" });
} else {
response.send(JSON.stringify({'authenticated':false}));
}
});
}
});
But that doesn't work. It says "Can't use mutable header APIs after sent" and puts it self in an endless loop saying "Can't render headers after they are sent to the client." over and over again.
Am I going about this the wrong way? I want my server code to connect with Facebook without the need of a page reload.