jwt-auth.rb

# application controller 

class ApplicationController < ActionController::API  
  before_action :authenticate 
  def logged_in?
    !!current_user
  end

  def current_user
    if auth_present?
      user = User.find(auth["user"])
      if user
        @current_user ||= user
      end
    end
  end

  def authenticate
    render json: {error: "unauthorized"}, status: 404 unless logged_in?
  end

  private
    def token
      request.env["HTTP_AUTHORIZATION"].scan(/Bearer(.*)$/).flatten.last.strip
    end

    def auth
      Auth.decode(token)
    end

    def auth_present?
      !!request.env.fetch("HTTP_AUTHORIZATION", "").scan(/Bearer/).flatten.first
    end
end

# auth.rb
# rake secret and store as AUTH_SECRET in application.yml using Figaro
require 'jwt'
class Auth
  ALGORITHM = 'HS256'
  def self.issue(payload)
    JWT.encode(
      payload,
      auth_secret,
      ALGORITHM)
  end
  
  def self.decode(token)
    JWT.decode(token, 
      auth_secret, 
      true, 
      { algorithm: ALGORITHM }).first
  end
  def self.auth_secret
    ENV["AUTH_SECRET"]
  end
end