Connect Local Users to Facebook/Twitter with PassortJS

I have an existing user base, that I want to allow them to link with their Facebook/Twitter Accounts. Looks like I can use passportjs but am having difficulty,

Right now, a url pass in their user/pass, I do a local stragety, and look up the user. Then I want to perform an authorize I presume. I get the facebook promopts asking if I want to allow, and I hit the callback with the accessToken, but I have no way to tie that token to an existing user in my db as I see now way to get the request info.

passport.serializeUser(function(user, done) {
  done(null, user);
});

passport.deserializeUser(function(user, done) {
    Users.findOne({_id: user._id}, function(err, user) {
        return done(err, user);
    });
});

passport.use(new LocalStrategy({ passReqToCallback: true }, function(req, username, password, done) {
        Users.findOne({_id: username}, function(err, user) {
            return done(null, user);
        });
    }
));


passport.use(new FacebookStrategy({
    clientID: 'xxxx',
    clientSecret: 'xxxx',
    callbackURL: "http://xxxx/facebook/callback",
    passReqToCallback: true
  },
  function(req, accessToken, refreshToken, profile, done) {

    //  How would I get access to the user found in the LocalStrategy here so I can associate the accessToken to the user in the db?
    console.log(accessToken);
    console.log(refreshToken);

    var err = null;
    var user = {};
    return done(err, user);

  }
));

server.get('/facebook', passport.authenticate('local', { failureRedirect: '/login', failureFlash: true }),
    function (req, res) {
        if (req && req.user) {
            passport.authorize('facebook', { scope: ['publish_actions','manage_pages'] })(req, res);
        }
});

server.get('/facebook/callback',
  passport.authorize('facebook', { failureRedirect: '/facebook/failure', successRedirect: '/facebook/success' }),
  function(req, res) {
    res.redirect('/');
  }
);