Has Users (JWT Auth with expiring session, registration/logging in), Columns that have Cards, Cards have Comments.
Requests to API described in Postman, first you need to register your account. It will give you a bearer token (Authorization header), which you should use in log in request. Also you'll need to use it in actions that require authentication (mostly everything except index/show actions.) Token expires in 30 minutes, after that you'll need to log in again.