error log

When you are for too long in business you think you know already everything and you are getting lazy. This happened to me again a few weeks ago. A customer asked me about the SQL Error Log Plugin. First I though he was talking about the MariaDB Error Log or the General Query Log. But then I have learned that there is something "new" I did not know yet...

We typically suggest our customers to use our MySQL/Galera Cluster my.cnf configuration template to avoid MySQL configuration and performance problems.

And we are paranoid as well. Thus we enable all useful logging:

wsrep_log_conflicts = 1

But this has also some consequences of more visibility...

Problem

A customer recently showed up with the following problem:

With your guidelines [ 1 ] I am now able to send the MySQL error log to the syslog and in particular to an external log server.
But I cannot see which user connects to the database in the error log.

How can I achieve this?

Idea

During night when I slept my brain worked independently on this problem and in the morning he had prepared a possible solution for it.