PhoneFactor is free for up to 25 users and reasonably priced after that. The beauty of PhoneFactor is that it utilizes something users already have – a mobile phone – as a token rather than a proprietary device.
PhoneFactor Agent, the software behind the service, acts as a RADIUS server for authentication to network resources such as a VPN. When a user attempts authentication, he will still first be prompted for a user name and password. After he enters those details, the service will place a call to his phone and require the user to answer the call and press the “#” button. Once this is completed, the user is successfully authenticated.
In this tutorial we will install the Agent on Windows Server 2008 R2, integrate with Active Directory, link a few user accounts, and set up a RADIUS server.