linux syslog messages

Hi,
I’m new with syslog messages on Linux OS and I have a small question.
I configure my syslog to create messages for “auth.*”.
Now when I log in the system I get the next message in my logs:

“pam_unix(login:session): session opened for user uri by LOGIN(uid=0)”

I wonder if control the message text?
Who create this message ?

Thanks