It is very easy but hard to find exact syntax. None of the current google top searches bring it out. You have to use mpm_itk module and exact example of syntax is here, enjoy!
<VirtualHost *:80> ServerName website.com DocumentRoot /var/www/website.com <IfModule mpm_itk_module> AssignUserId username groupname </IfModule> </VirtualHost>
In case you see error like this
Invalid command 'AssignUserId', perhaps misspelled or defined by a module not included in the server configuration Action 'configtest' failed. The Apache error log may have more information. ...fail!
Then install the mpm_itk module in ubuntu like this
sudo apt-get install apache2-mpm-itk