My envvar files has these lines in it:

export APACHE_RUN_USER=www-data
export APACHE_RUN_GROUP=www-data

My apache2.conf has these lines in it:

# These need to be set in /etc/apache2/envvars
User ${APACHE_RUN_USER}
Group ${APACHE_RUN_GROUP}

But when I run apache2 -M I get this:

apache2: bad user name ${APACHE_RUN_USER}

A temporary fix is to hard-code www-data into it my apache2.conf file. There was some speculation here that this was because some configuration script didn't replace the env vars correctly in my apache2.conf file. Regardless how do I get apache2 to consult my envvars file?

As another data point this site seems to indicate the envvars is generated at build, but read by apache2ctl at runtime, suggesting that this file isn't just poop leftover by the build process.