socket.io how to read client certificate

Can socket.io (on the server) read the SSL certificate from the client if the connection is done by a browser? I have an html-page that initiate a long polling to a node server. When the requet from the client comes to a node-app, node.js is able to read the client certificate with this code:

request.connection.getPeerCertificate()

However, Im trying to use sockets instead of longpolling.

In the socket-function on node-app I have this:

io.sockets.on('connection', function (socket) {

However, inside this function I cannot use

request.connection.getPeerCertificate()

as there is not any "request" object here. What is coming in is the socket from the cient. I have outputted in the console all the content of the socket but I cannot see any field that correspond to

request.connection.getPeerCertificate()

Is there a way to "force" the socket on the client to also include the certificate/key when connecting to the server?

I have found a few resources about this issue. For example here.

Most of the comments seem to tell about socket.io not beeing able to read the certificate on the connected client. The first post looks llike a work around. But I dont really understand how to implement that. Tjhere is no "io.Manager" in socket.io-source code. If I output "io.Manager" to the console I then get an "undefined"