jwt_sessions

XSS/CSRF safe JWT auth designed for SPA

Table of Contents

• Synopsis
• Installation
• Getting Started
  • Rails integration
  • Non-Rails usage
• Configuration
  • Redis
  • JWT signature
  • Request headers and cookies names
  • Expiration time
  • CSRF and cookies
  • Refresh with access token
  • Refresh token hijack protection
• Flush Sessions
  • Sessions Namespace
  • Logout
• Examples
• Contributing
• License

Synopsis

Main goal of this gem is to provide configurable, manageable, and safe stateful sessions based on JSON Web Tokens.

It's designed to be framework agnostic yet is easily integrable so Rails integration is also available out of the box.

Core concept behind jwt_sessions is that each session is represented by a pair of tokens: access and refresh, and a session store is used to handle CSRF checks and refresh token hijacking. Both tokens have configurable expiration times, but in general refresh token is supposed to have a longer lifespan than an access token. Access token is used to retrieve secured resources and refresh token is used to renew the access token once it's expired. Default token store is based on redis.

All tokens are encoded and decoded by ruby-jwt gem, and its reserved claim names are supported as well as it's allowed to configure claim checks and cryptographic signing algorithms supported by it. jwt_sessions itself uses ext claim and HS256 signing by default.

Installation

Put this line in your Gemfile

gem 'jwt_sessions'

Then run

bundle install

Getting Started

Authorization mixin is supposed to be included in your controllers and is used to retrieve access and refresh tokens from incoming requests and verify CSRF token if needed. It assumes that a token is either in a cookie or in a header (cookie and header names are configurable). It tries to retrieve it from headers first, then from cookies (CSRF check included) if the headers check failed.

Rails integration

Include JWTSessions::RailsAuthorization in your controllers, add JWTSessions::Errors::Unauthorized exceptions handling if needed.

class ApplicationController < ActionController::API
  include JWTSessions::RailsAuthorization
  rescue_from JWTSessions::Errors::Unauthorized, with: :not_authorized

  private

  def not_authorized
    render json: { error: 'Not authorized' }, status: :unauthorized
  end
end

Specify an encryption key for JSON Web Tokens in config/initializers/jwt_session.rb \ It's adviced to store the key itself within the app secrets.

JWTSessions.algorithm = 'HS256'
JWTSessions.encryption_key = Rails.application.secrets.secret_jwt_encryption_key

Most of the encryption algorithms require private and public keys to sign a token, yet HMAC only require a single key, so you can use a shortcat encryption_key to sign the token. For other algorithms you must specify a private and public keys separately.

JWTSessions.algorithm   = 'RS256'
JWTSessions.private_key = OpenSSL::PKey::RSA.generate(2048)
JWTSessions.public_key  = JWTSessions.private_key.public_key

Generate access/refresh/csrf tokens with a custom payload. \ The payload will be available in the controllers once the access (or refresh) token is authorized. \ Access/refresh tokens contain expiration time in their payload. Yet expiration times are also added to the output just in case.

> payload = { user_id: user.id }
=> {:user_id=>1}

> session = JWTSessions::Session.new(payload: payload)
=> #<JWTSessions::Session:0x00007fbe2cce9ea0...>

> session.login
=> {:csrf=>"BmhxDRW5NAEIx...",
    :access=>"eyJhbGciOiJIUzI1NiJ9...",
    :access_expires_at=>"..."
    :refresh=>"eyJhbGciOiJIUzI1NiJ9...",
    :refresh_expires_at=>"..."}

You can build login controller to receive access, refresh and csrf tokens in exchange for user's login/password. \ Refresh controller - to be able to get a new access token using refresh token after access is expired. \ Here is example of a simple login controller, which returns set of tokens as a plain JSON response. \ It's also possible to set tokens as cookies in the response instead.

class LoginController < ApplicationController
  def create
    user = User.find_by!(email: params[:email])
    if user.authenticate(params[:password])
      payload = { user_id: user.id }
      session = JWTSessions::Session.new(payload: payload)
      render json: session.login
    else
      render json: 'Invalid user', status: :unauthorized
    end
  end
end

Since it's not required to pass an access token when you want to perform a refresh you may need to have some data in the payload of the refresh token to allow you to construct a payload of the new access token during refresh.

session = JWTSessions::Session.new(payload: payload, refresh_payload: refresh_payload)

Now you can build a refresh endpoint. To protect the endpoint use before_action authorize_refresh_request!. \ The endpoint itself should return a renewed access token.

class RefreshController < ApplicationController
  before_action :authorize_refresh_request!

  def create
    session = JWTSessions::Session.new(payload: access_payload)
    render json: session.refresh(found_token)
  end

  def access_payload
    # payload here stands for refresh token payload
    build_access_payload_based_on_refresh(payload)
  end
end

In the example found_token - is a token fetched from request headers or cookies. In the context of RefreshController it's a refresh token. \ The refresh request with headers must include X-Refresh-Token (header name is configurable) with refresh token.

X-Refresh-Token: eyJhbGciOiJIUzI1NiJ9...
POST /refresh

Now when there're login and refresh endpoints, you can protect the rest of your secure controllers with before_action :authorize_access_request!.

class UsersController < ApplicationController
  before_action :authorize_access_request!

  def index
    ...
  end

  def show
    ...
  end
end

Headers must include Authorization: Bearer with access token.

Authorization: Bearer eyJhbGciOiJIUzI1NiJ9...
GET /users

The payload method is available to fetch encoded data from the token.

def current_user
  @current_user ||= User.find(payload['user_id'])
end

Non-Rails usage

You must include JWTSessions::Authorization module to your auth class and implement within it next methods:

1. request_headers

def request_headers
  # must return hash-like object with request headers
end

1. request_cookies

def request_cookies
  # must return hash-like object with request cookies
end

1. request_method

def request_method
  # must return current request verb as a string in upcase, f.e. 'GET', 'HEAD', 'POST', 'PATCH', etc
end

Example Sinatra app. \ NOTE: Since rack updates HTTP headers by using HTTP_ prefix, upcasing and using underscores for sake of simplicity JWTSessions tokens header names are converted to rack-style in this example.

require 'sinatra/base'

JWTSessions.access_header = 'authorization'
JWTSessions.refresh_header = 'x_refresh_token'
JWTSessions.csrf_header = 'x_csrf_token'
JWTSessions.encryption_key = 'secret key'

class SimpleApp < Sinatra::Base
  include JWTSessions::Authorization

  def request_headers
    env.inject({}){|acc, (k,v)| acc[$1.downcase] = v if k =~ /^http_(.*)/i; acc}
  end

  def request_cookies
    request.cookies
  end

  def request_method
    request.request_method
  end

  before do
    content_type 'application/json'
  end

  post '/login' do
    access_payload = { key: 'access value' }
    refresh_payload = { key: 'refresh value' }
    session = JWTSessions::Session.new(payload: access_payload, refresh_payload: refresh_payload)
    session.login.to_json
  end

  # POST /refresh
  # x_refresh_token: ...
  post '/refresh' do
    authorize_refresh_request!
    access_payload = { key: 'reloaded access value' }
    session = JWTSessions::Session.new(payload: access_payload, refresh_payload: payload)
    session.refresh(found_token).to_json
  end

  # GET /payload
  # authorization: Bearer ...
  get '/payload' do
    authorize_access_request!
    payload.to_json
  end

  # ...
end

Configuration

List of configurable settings with their default values.

Redis

Default token store configurations

JWTSessions.redis_host    = '127.0.0.1'
JWTSessions.redis_port    = '6379'
JWTSessions.redis_db_name = '0'
JWTSessions.token_prefix  = 'jwt_' # used for redis db keys

You can also provide a Redis URL instead:

JWTSessions.redis_url = 'redis://localhost:6397'

NOTE: if REDIS_URL environment variable is set it is used automatically.

JWT signature

JWTSessions.algorithm = 'HS256'

You need to specify a secret to use for HMAC, this setting doesn't have a default value.

JWTSessions.encryption_key = 'secret'

If you are using another algorithm like RSA/ECDSA/EDDSA you should specify private and public keys.

JWTSessions.private_key = 'abcd'
JWTSessions.public_key  = 'efjh'

NOTE: ED25519 and HS512256 require rbnacl installation in order to make it work.

jwt_sessions only uses exp claim by default when it decodes tokens, you can specify which additional claims to use by setting jwt_options. You can also specify leeway to account for clock skew.

JWTSessions.jwt_options.verify_iss = true
JWTSessions.jwt_options.verify_sub = true
JWTSessions.jwt_options.verify_iat = true
JWTSessions.jwt_options.verify_aud = true
JWTSessions.jwt_options.leeway     = 30 # seconds

To pass options like sub, aud, iss, or leeways you should specify a method called token_claims in your controller.

class UsersController < ApplicationController
  before_action :authorize_access_request!

  def token_claims
    {
      aud: ['admin', 'staff'],
      exp_leeway: 15 # will be used instead of default leeway only for exp claim
    }
  end
end

Claims are also supported by JWTSessions::Session, you can pass access_claims and refresh_claims options in the initializer.

Request headers and cookies names

Default request headers/cookies names can be re-configured

JWTSessions.access_header  = 'Authorization'
JWTSessions.access_cookie  = 'jwt_access'
JWTSessions.refresh_header = 'X-Refresh-Token'
JWTSessions.refresh_cookie = 'jwt_refresh'
JWTSessions.csrf_header    = 'X-CSRF-Token'

Expiration time

Access token must have a short life span, while refresh tokens can be stored for a longer time period

JWTSessions.access_exp_time = 3600 # 1 hour in seconds
JWTSessions.refresh_exp_time = 604800 # 1 week in seconds

CSRF and cookies

In case when you use cookies as your tokens transport it gets vulnerable to CSRF. That's why both login and refresh methods of the Session class produce CSRF tokens for you. Authorization mixin expects that this token is sent with all requests except GET and HEAD in a header specified among this gem's settings (X-CSRF-Token by default). Verification will be done automatically and Authorization exception will be raised in case of mismatch between the token from the header and the one stored in session. \ Although you don't need to mitigate BREACH attacks it's still possible to generate a new masked token with the access token.

session = JWTSessions::Session.new
session.masked_csrf(access_token)

Refresh with access token

Sometimes it's not secure enough to store the refresh tokens in web / JS clients. \ That's why you have a possibility to operate only by an access token, and to not pass the refresh to the client at all. \ Session accepts refresh_by_access_allowed: true setting, which links the access token to the according refresh token. \ Example Rails login controller, which passes an access token token via cookies and renders CSRF.

class LoginController < ApplicationController
  def create
    user = User.find_by!(email: params[:email])
    if user.authenticate(params[:password])

      payload = { user_id: user.id }
      session = JWTSessions::Session.new(payload: payload, refresh_by_access_allowed: true)
      tokens = session.login
      response.set_cookie(JWTSessions.access_cookie,
                          value: tokens[:access],
                          httponly: true,
                          secure: Rails.env.production?)

      render json: { csrf: tokens[:csrf] }
    else
      render json: 'Invalid email or password', status: :unauthorized
    end
  end
end

The gem provides an ability to refresh the session by access token.

session = JWTSessions::Session.new(payload: payload, refresh_by_access_allowed: true)
tokens  = session.refresh_by_access_payload

In case of token forgery and successful refresh performed by an atacker - the original user will have to logout. \ To protect the endpoint use before_action authorize_refresh_by_access_request!. \ Example Rails refresh by access controller with cookies as token transport. \ As refresh should be performed once the access token is already expired we need to use claimless_payload method in order to skip JWT expiration validation (and other claims) so we can proceed.

class RefreshController < ApplicationController
  before_action :authorize_refresh_by_access_request!

  def create
    session = JWTSessions::Session.new(payload: claimless_payload, refresh_by_access_allowed: true)
    tokens  = session.refresh_by_access_payload
    response.set_cookie(JWTSessions.access_cookie,
                        value: tokens[:access],
                        httponly: true,
                        secure: Rails.env.production?)

    render json: { csrf: tokens[:csrf] }
  end
end

Refresh token hijack protection

There is a security recommendation regarding the usage of refresh tokens: only perform refresh when an access token gets expired. \ Since sessions are always defined by a pair of tokens and there can't be multiple access tokens for a single refresh token simultaneous usage of the refresh token by multiple users can be easily noticed as refresh will be perfomed before the expiration of the access token by one of the users. Because of that refresh method of the Session class supports optional block as one of its arguments which will be executed only in case of refresh being performed before the expiration of the access token.

session = JwtSessions::Session.new(payload: payload)
session.refresh(refresh_token) { |refresh_token_uid, access_token_expiration| ... }

Flush Sessions

Flush a session by its refresh token. The method returns number of flushed sessions.

session = JWTSessions::Session.new
tokens = session.login
session.flush_by_token(tokens[:refresh]) # => 1

Flush a session by its access token.

session = JWTSessions::Session.new(refresh_by_access_allowed: true)
tokens = session.login
session.flush_by_access_payload
# or
session = JWTSessions::Session.new(refresh_by_access_allowed: true, payload: payload)
session.flush_by_access_payload

Or by refresh token UID

session.flush_by_uid(uid) # => 1

Sessions namespace

It's possible to group sessions by custom namespaces

session = JWTSessions::Session.new(namespace: 'account-1')

and selectively flush sessions by namespace

session = JWTSessions::Session.new(namespace: 'ie-sessions')
session.flush_namespaced # will flush all sessions which belong to the same namespace

it's posible to flush access tokens only

session = JWTSessions::Session.new(namespace: 'ie-sessions')
session.flush_namespaced_access_tokens # will flush all access tokens which belong to the same namespace, but will keep refresh tokens

To force flush of all app sessions

JWTSessions::Session.flush_all

Logout

To logout you need to remove both access and refresh tokens from the store. \ Flush sessions methods can be used to perform logout. \ Refresh token or refresh token UID is required to flush a session. \ To logout with an access token refresh_by_access_allowed setting should be set to true on an access token creation. If logout by access token is allowed it's recommended to ignore the expiration claim and to allow to logout with expired access token.

Examples

Rails API \ Sinatra API

You can use a mixed approach for the cases when you'd like to store an access token in localStorage and refresh token in HTTP-only secure cookies. \ Rails controllers setup example:

class LoginController < ApplicationController
  def create
    user = User.find_by(email: params[:email])
    if user&.authenticate(params[:password])

      payload = { user_id: user.id, role: user.role, permissions: user.permissions }
      refresh_payload = { user_id: user.id }
      session = JWTSessions::Session.new(payload: payload, refresh_payload: refresh_payload)
      tokens = session.login
      response.set_cookie(JWTSessions.refresh_cookie,
                          value: tokens[:refresh],
                          httponly: true,
                          secure: Rails.env.production?)

      render json: { access: tokens[:access], csrf: tokens[:csrf] }
    else
      render json: 'Cannot login', status: :unauthorized
    end
  end
end

class RefreshController < ApplicationController
  before_action :authorize_refresh_request!

  def create
    tokens = JWTSessions::Session.new(payload: access_payload).refresh(found_token)
    render json: { access: tokens[:access], csrf: tokens[:csrf] }
  end

  def access_payload
    user = User.find_by!(email: payload['user_id'])
    { user_id: user.id, role: user.role, permissions: user.permissions }
  end
end

class ResourcesController < ApplicationController
  before_action :authorize_access_request!
  before_action :validate_role_and_permissions_from_payload

  # ...
end

Contributing

Fork & Pull Request. \ RbNaCl and sodium cryptographic library are required for tests.

For MacOS see these instructions. \ For example, with Homebrew:

brew install libsodium

License

MIT