token.rb

require 'jwt'

module TrackerFlow
  module Web
    module Auth
      class Token
        class InvalidToken < StandardError; end

        PRIVATE_KEY = ENV['JWT_PRIVATE_KEY'] || fail('no private key found')
        KEY = OpenSSL::PKey::RSA.new(PRIVATE_KEY)

        def self.parse(token)
          payload, _header = JWT.decode(token, KEY.public_key, true, { :algorithm => 'RS256' })
          new(user_id: payload['sub'])
        rescue JWT::DecodeError => e
          fail InvalidToken, e
        end

        def initialize(user: nil, user_id: nil)
          fail ArgumentError, 'either user or user_id is required' if user.nil? && user_id.nil?
          @user_id = user&.id || user_id
        end

        def user_id
          @user_id.to_i
        end

        def generate
          subject = @user_id
          payload = { sub: subject }
          JWT.encode(payload, KEY, 'RS256')
        end
      end
    end
  end
end