This is a small script that allows authentication of OpenVPN clients against an NextCloud instance. (May also work with Owncloud, but never tested)
Place the openvpn-nextcloud-auth.py script into the working directory of your OpenVPN server and configure the base_url in the script.
With the auth-user-pass-verify setting you can instruct OpenVPN to call this script each time a client tries to authenticate. There are two ways how OpenVPN publishes the clients credentials to the script. Either with environment variables or with a temporary file. The script supports both methods.
Update your OpenVPN configuration:
Environment variables:
auth-user-pass-verify openvpn-nextcloud-auth.py via-env
script-security 3
Adjusting the script-security setting is mandatory if you use the "environment variable" way, see https://community.openvpn.net/openvpn/ticket/747
Temporary file: (Recommended)
auth-user-pass-verify openvpn-nextcloud-auth.py via-file