CUA (Central User Administration) and logging of changes

Question: We use central user administration with about 50 client-systems. we want to logg all changes in SU01 in the master system (also including the changes which will be done in the client-systems !).
We have 2 approaches :
1. User-Exit in SU01 : does there is such an exit ? we have found nothing
2. Logging of IDOC-Informations (if possible also with user-Exit, perhaps in IDOC-Processing).

What will be the best and easiest way (also regarding upgrades and so on).

Siggi

Answer:
1. yes it exist but not via SMOD, it is a record entry in SSM_CUST.
2. IDOC info is already captured use BD87 to look at the info, note there is an idoc for every client in every system even though one client is used, CUA is not realy designed for more than one client "workplace" and R/3.
3. THe change history is already capture for you and avilable in the history reports of SUIM.