Two Factor - Virtual Private Network

["self.away" <self.away () gmail com>]

Hi.
I'm trying to setup a remote access vpn (user dials up from home to
our vpn server).The first goal was to set up a pptp vpn based on
microsoft rras which turned out pretty easy.
Now it has been required to add an extra layer of security to vpn
authentication by adding a certificate which as far as i read it
should be accomplished adding EAP authentication to our vpn pptp
configuration.
However it seems when adding EAP to vpn pptp ,authentication login to
our VPN will only require certificate installed on remote vpn user
workstation and not user/password.
How can i get both user/password and certificate in the authentication
process for vpn pptp with microsoft rras?
Is there any other opensource vpn solution based on two-factor authentication?

Thank you

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