vpn-user-portal since version 1.0.3, supports Basic authentication to obtain configurations.
$ curl -u foo:bar -d 'name=agent007' http://localhost/vpn-user-portal/config/
$ curl -u foo:bar http://localhost/vpn-user-portal/config/agent007/ovpn
...
... OpenVPN config
...
Also supported is retrieving a ZIP version of the configuration by specifying /zip instead of /ovpn.
Packages for RHEL/CentOS/Fedora can be obtained in this COPR repository.