Running external programs

Hi, all. We have some legacy software that ran under XTradius (xtradius.sourceforge.net). The important thing was to execute an external program for every auth & accounting request. Now I need to recreate all that on another server, and I must use the same legacy billing software. Unfortunately one can no longer build the old XTradius on modern FreeBSDs, apparently it has some variable linkage problems. Can that simple task be done in FreeRADIUS instead? Can it be configured to call an external program (Auth-Type "External" in XTradius)? Thanks!