How use AD for authorization and radius for two-factor auth
http://www.wikidsystems.com/support/wikid-support-center/how-to/how-to-add-two-factor-authentication-to-npsDid you know that Microsoft can proxy authentication requests to a 3rd party server? The MS radius plugin NPS will allow user to login with an AD username and an OTP, preform authorization based on the username and proxy the creds for authentication.