Thanks Julian, it works!
For anyone else that wants to do this I've attached my config.json file below:
{ "url": "http://localhost/forum", "port": "/tmp/nodeenv.sock", "secret": "random-secret-here", "database": "mongo", "mongo": { "host": "127.0.0.1", "port": "27017", "username": "", "password": "", "database": "0" } }