HID ActivID 4TRESS AS and Citrix XenApp - Manual (Page 7)

ActivIdentity 4TRESS Authentication Server | Handbook: Configuring Citrix® XenApp™ for Two-Factor Authentication P 7
External Use | May 31, 2012 | © 2012 ActivIdentity
12. In the tree to the left, expand Explicit, and then click Two-Factor Authentication.
13. From the Two-factor setting drop-down menu, select RADIUS.
14. Add a RADIUS Server with a Server address and Server port, and then click OK.