Pre-requisite: PDO-compatible DB server; PHP compiled with a PDO DB extension

1. Set up external DB auth with your PDO-compatible server, and use the "pdo" option for connection. You will need to configure the connect string in the host setting to something like:pgsql:host=localhost;port=5432;dbname=enroltest
2. Ensure you can log in and all information is loaded as expected.
3. Set up external DB enrolment against the same PDO option.
4. Ensure users are enrolled as expected.