...
You can use any direct link to link to your APK/OBB files. You can also use popular hosting providers like Google Drive and Drop Box if you alter the url slightly to make the file automatically download.
Google Drive:
https://drive.google.com/file/d/1yPgVWvvvSxu6ikVJOqzyvTOMXAm-Dv9x/view
becomes
https://drive.google.com/uc?id=1yPgVWvvvSxu6ikVJOqzyvTOMXAm-Dv9x&export=download
Drop Box:
https://www.dropbox.com/s/gsfgjg2g24gj42/MyCoolApp.apk
...