After adjust the verbosity of the parameter "accessControl" with the command:
'db.setLogLevel(5,"accessControl")'
The log file still not login successful login.
On mongo 3.2:
2017-04-20T15:56:06.661+0200 I ACCESS [conn16895093] Successfully authenticated as principal username on admin
On mongo 3.4:
Only unsuccessful auth like:
2017-04-25T15:07:04.478+0200 I ACCESS [conn291586] SCRAM-SHA-1 authentication failed for username on admin from client 127.0.0.1:37171 ; AuthenticationFailed: SCRAM-SHA-1 authentication failed, storedKey mismatch
So I can NOT upgrade my environment from 3.2 to 3.4 safely.
Best Regards