1. Download DUO Proxy Authenticator. Use the default installation instructions and you will notice that DUO service is not running in services.msc. This is expected, because authproxy.conf has to be configured for your environment.
2. Open Windows Explorer, navigate to C:\Program Files (x86)\Duo Security Authentication Proxy\conf and open authproxy.conf.
3. The configuration file has several unnecessary settings and for RAS integration we should configure the following:
4. Start DUO Security Authentication proxy Service:
5. Configure RAS to communicate with DUO: RAS Console > Farm > Connections > Second Level Authentication Tab. Chose the option to use RADIUS and click on Settings:
6. Configure connection settings:
7. Click on Check Connection and you should see Success result:
8. Click Apply and the next time users logon they will have 2-factor-authentication enabled.