When using one or more packages that declare a Mongo collection (for example accounts-base), it isn't possible to call Mongo.setConnectionOptions in the main app code or imports directory. The only workaround is to create a new local package containing the configuration and place it above accounts-base in the packages file.

It would be good to have to option to put the settings in settings.json somehow although I'm not sure how that would work with importing PEM files (e.g. the sslCA option).