Apache2 authentication with mod_authn_dbd and MySQL

Following this howto I tried to set up my Debian 8 server with Apache 2.4.10 and MySQL 5.5.50 to use MySQL as authentication backend for my SVN. I get an internal server error and can't figure out why.

First I added the file /etc/apache2/conf-available/dbd_mysql.conf, containing

<IfModule mod_dbd.c>
    DBDriver        mysql
    DBDParams       "host=localhost user=THEUSER pass=THEPASS"
    DBDMin          2
    DBDKeep         4
    DBDMax          10
    DBDExptime      300
</IfModule>

of course followed by

a2enconfig dbd_mysql

I've set up a MySQL Database "authdb" containing the table "mysql_auth" with basically two important columns, "username" and "password". The specific database is accessible by a user, which I will refer to as "THEUSER" with SELECT permission.

Then I added the site specific configuration in /etc/apache2/site-available/svn.conf:

DBDParams "dbname=authdb"

<Location /svn/private/>

    DAV svn
    SVNParentPath /svn/private/
    AuthzSVNAccessFile /svn/auth/accesslist_private

    SSLRequireSSL
    AuthUserFile /dev/null
    AuthName "SVN"
    AuthType Basic
    <IfModule mod_authn_dbd.c>

            AuthBasicProvider dbd
            AuthDBDUserPWQuery "SELECT password FROM mysql_auth WHERE username = %s"
            Require valid-user

    </IfModule>
</Location>

This site configuration has already been enabled so I restarted the Apache and found something in the log file which I absolutely can not understand:

[dbd:error] [pid 15225] (20014)Internal error: AH00629: Can't connect to mysql: Access denied for user 'A LOCAL SYSTEM USER'@'localhost' (using password: NO)
[dbd:error] [pid 15225] (20014)Internal error: AH00633: failed to initialise
[authn_dbd:error] [pid 15225] [client XX.XX.XX.XX:XYZ] AH01653: Failed to acquire database connection to look up user 'some_user'

This error repeats whenever I try to access my SVN repository.

What is really strange about this is that there is a user in the log file which I absolutely do not expect to find here. It is a system user who as nothing to do with neither MySQL nor Apache. This user is only used to login with SSH. Which point am I missing? Any help would be appreciated!

Solution

Finally figured out the problem. Obviously the content of my configuration file was loaded after the content of my site definition.

The solution was as follows: I moved the content from dbd_mysql.conf right in front of the -Definition of my /etc/apache2/site-available/svn.conf, disabled the conf, reloaded Apache and everything worked.

What I haven't figured out yet is, if my configuration is faulty because I would have expected that the configuration is loaded before my site definition which relies on the previous configuration.