Issue Apache user changes with directive. - Why?

[Sebastian]

When I run a simple php web page that echos out the apache user with

echo exec('whoami');

it gives me the expected system user, e.g.

bob

When I run the same but with an alias directive in apache settings:

AliasMatch /appname(/.*)? /var/www/vhosts/domain.dev/httpdocs/apps/appname/$1
Alias /appname /var/www/vhosts/domain.dev/httpdocs/apps/appname
<Directory "/var/www/vhosts/domain.dev/httpdocs/apps/appname">
    <IfModule sapi_apache2.c>
        php_admin_flag engine on
    </IfModule>
    <IfModule mod_php7.c>
        php_admin_flag engine on
    </IfModule>
</Directory>

the user changes to

www-data

Question: Why? And how can I avoid this?

 

[IgorG]

Question: Why? And how can I avoid this?

I think that explanation in this thread could be interesting for you Resolved - apache run whit customer user not whit www-data

 

[Sebastian]

I think that explanation in this thread could be interesting for you Resolved - apache run whit customer user not whit www-data

I read this before, but it does not help here.
What UFHH01 points out there is a warning not to mess around with config files to force apache to use another user. And I can second that.
E.g. I have played around with /etc/apache2/envvars and changed the APACHE_RUN_USER and APACHE_RUN_GROUP, but that (at least) broke the Plesk log file viewer, so I had to reverse it.