Just a quick reference on how to make a directory writable by OSX integrated Apache web server.
1. Set the ownership of your desired directory/file to the _www user:
sudo chown -R _www:staff path/to/folder/
2. Set the permissions so that the _www can write in the directory/file without giving permissions to everyone else:
sudo chmod -R 755 path/to/folder
Happy coding 🙂