Auth provider allowed authorisation base on external site users for phpBB 3.1
Clone into phpBB folder /ext/darkdiesel/authproviderexternalsite:
git clone git@github.com:darkdiesel/phphBB-AuthProvider-ExternalSite.git phpBB folder /ext/darkdiesel/authproviderexternalsite
Go to "ACP" > "Customise" > "Extensions" and enable the "Auth Provider Other Site" extension.