I'm using express.js and i need to know the domain which is originating the call. This is the simple code

    app.get(
        '/verify_license_key.json',
        function( req, res ) {
        	// do something

How do i get the domain from the `req` or the `res` object?
I mean i need to know if the api was called by somesite.com or someothersite.com. 
I tried doing a console.dir of both `req` and `res` but i got no idea from there, also read the documentation but it gave me no help.