MacOS – Fix permissions in Apache

I'm trying to use the built-in Apache server in MacOS mojave.

In my browser, accessing http://localhost/~myusername/mypage.html (in case of user dir) or http://localhost/mypage.html (in case of default dir) both throw the same error in the browser:

Forbidden You don't have permission to access /mysite/ on this server.

I' trying to make both the default dir /Library/WebServer/Documents and an user dir ~/myusername/Sitesworks.
I tried 2 solutions:

1. I tried to add a vhost in /etc/apache2/extra/httpd-vhosts.conf

   <VirtualHost *:80>
   ServerName localhost
   DocumentRoot /Library/WebServer/Documents/
   </VirtualHost>
   

2. I tried to add a myusername.conf file in /etc/apache2/users with the following content

   <Directory "/Users/myusername/Sites/">
   Options Indexes MultiViews
   AllowOverride All
   Order allow,deny
   Allow from all
   </Directory>
   

Is there a guide to understanding permission errors on Mojave using Apple shipped Apache?

EDIT: It looks like the accepted answer here solved the reading permission for me.
From the answer:

1. Load the module mod_userdir in /etc/apache2/httpd.conf
2. At the end of the httpd.conf make sure to load httpd-userdir.conf
3. In httpd-userdir.conf include a local file in /etc/apache2/users/<username>.conf

4. Put a directory section into that file, containing the rules for the directory where your webserver files are located:

     <Directory "/Users/<myusername>/Sites/">
         AllowOverride All
         Options Indexes FollowSymLinks
         Require all granted
     </Directory>
   

Writing access to files is still a problem: Apache cannot edit a file if the ownership is mine (the admin user). I'm still wondering if there is a proper way to fix the permission without messing up each directory permissions every new project.

This is the script I'm using for testing write permission:

<?php
    echo 'Current script owner: ' . get_current_user();
    echo 'Current user:' . system('whoami');
    $current = file_get_contents('people.txt');
    $current .= "John Smith\n";
    file_put_contents($file, $current);

I get the error:

Warning: file_put_contents(people.txt): failed to open stream:
Permission denied