title: Rails: authenticate with JWT Token using knock
body: <p>Iam trying to build an authentication solution for my app. Iam using React as frontend and Rails in API mode as my backend. I have an external authentication solution, which I need to use. I stumbled over Knock for JWT token management but I dont understand the documentation, especially this part "It must have an authenticate method, similar to the one added by has_secure_password.", since, due to my external authentication service, i dont have a User Model.
  So in my head, a login request would go to my LoginController, which would manage the external authentication, and, after successful authentication, would somehow create an JWT token and return this to the frontend.
  Any idea how i achieve this?</p>