How can I set a custom field in POST header on submit a form?
In fact a better way to do it to save a cookie on the client side. Then the cookie is automatically sent with every page header for that particular domain.
In node-js, you can set up and use cookies with cookie-parser.
an example:
res.cookie('token', "xyz....", { httpOnly: true });
Now you can access this :
app.get('/',function(req, res){
var token = req.cookies.token
});
Note that httpOnly:true ensures that the cookie is usually not accessible manually or through javascript and only browser can access it.
If you want to send some headers or security tokens with a form post, and not through ajax, in most situation this can be considered a secure way. Although make sure that the data is sent over secure protocol /ssl if you are storing some sensitive user related info which is usually the case.