Using the CORS module of node for dynamic origins

gistfile1.js

var cors = require('cors')

var whitelist = ['http://localhost:4000','http://someotherserver.com'];

var corsOptions = {
  origin: function(origin, callback){
    var originIsWhitelisted = whitelist.indexOf(origin) !== -1;
    callback(null, originIsWhitelisted);
  }
};

app.options('/chans',cors(corsOptions))


app.put('/chans',cors(),function(req,resp){
})