All that sa_post_login_procedure does is to check whether userID is about to expire.
From what you described in your first reply,
if this is what you really want :
"Basically, I need to know how I could trigger an insert statement on any db connection, so I could know how many connections are being made at the same time"
Then you can use procedure profiling by first calling and enabling the procedure and
selecting on particular stored procedure:
i.e. select * from sa_procedure_profile where object_type = 'p' and object_name = '<user-defined store procedure>';
Here is the link for all the properties that can be used for procedure profiling :
http://dcx.sap.com/index.html#sa160/en/dbreference/sa-procedure-profile-system-procedure.html
I hope I didnt misunderstand you this time.