The user is nbrm in the line shown. If that's not indicative of who is logging in, then that's an issue with your deployment.
If you additionally want to know which client user account the user is logging in from, I don't suspect that is possible. You can snoop the HTTP headers, but I don't believe that information is present there. If it is, then you can should be able to customize Apache's log file format to include that information.