Rails.application.routes.draw do
  devise_for :users, :controllers => {sessions: 'sessions', registrations: 'registrations'}
end

class RegistrationsController < Devise::RegistrationsController
    respond_to :json
end

class SessionsController < Devise::SessionsController
    respond_to :json
end

{
    user: {
        email: [email protected],
        password: password,
        password_confirmation: password
    }
}

Started POST "/users" for 23.233.9.94 at 2016-12-22 08:22:11 +0000
Processing by RegistrationsController#create as */*
  Parameters: {"Payload: {  rn    user: {rn        email: [email protected],rn        password: password,rn        password_confirmation: passwordrn    }rn}"=>"[FILTERED]"}
   (0.2ms)  begin transaction
   (0.1ms)  rollback transaction
Completed 200 OK in 5ms (Views: 0.2ms | ActiveRecord: 0.3ms)

{
    "user": {
        "email": "[email protected]",
        "password": "password",
        "password_confirmation": "password"
    }
}