As psychobunny suggests with the referenced links, you cant elaborate your own SSO plugin to gain acces from nodeBB to the user stored on your own database, making your Rails system to act as the SSO provider.
The other link is the write API nodebb provides. You would have to install this plugin in order to have it working.
@Nguyen-Nga That particular problem is due to a query we want to run against socket.io being unavailable in the latest version. It presents when used in a clustering setup, and the latest changes to NodeBB always have clustering active (even in a cluster setup of 1 process), so in the meantime it is difficult to get the data in question. This is why those graphs are not working at the moment.