In a computer implemented method, a client computer connected to a public network such as the Internet makes a request for an intranet resource to a tunnel of a firewall isolating the intranet from the Internet. The request is made in a public message. The tunnel sends a message to the client computer to redirect to a proxy server of the tunnel. The client computer send a token and the request for the resource the proxy server. If the token is valid, the request is forwarded to the intranet, otherwise, the user of the client computer must first be authenticated.