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1) OTP + authentication server? Yes. We use it with AD and LDAP.
2) OTP + Radius? Presumably, but I have not tried it.
3) Radius determines OTP? If you do not want to use the UTM token system and its interface, you need to build your own user interface, or buy it. Depends somewhat on how you want to enroll users in 2FA, and what types of 2FA methods you want to support. Generally if you don't want UTM's free solution, you probably want to consider DUO.
1) OTP + authentication server? Yes. We use it with AD and LDAP.
2) OTP + Radius? Presumably, but I have not tried it.
3) Radius determines OTP? If you do not want to use the UTM token system and its interface, you need to build your own user interface, or buy it. Depends somewhat on how you want to enroll users in 2FA, and what types of 2FA methods you want to support. Generally if you don't want UTM's free solution, you probably want to consider DUO.