This is just a copy/paste from the manual on how to set up Database as your user backend.
NOTE that this is not the only choice, but the simplest
Instead of doing all of the node osjs config:set
you can make your own file in src/conf/
(ex src/conf/901-my-config.json
), but this is optional.
After setup and rebuild, estart your client and server and you should be able to log in :)