Devise::JWT

devise-jwt is a devise extension which uses JWT tokens for user authentication. It follows secure by default principle.

This gem is just a replacement for cookies when these can't be used. As cookies, a token expired with devise-jwt will mandatorily have an expiration time. If you need that your users never sign out, you will be better off with a solution using refresh tokens, like some implementation of OAuth2.

You can read about which security concerns this library takes into account and about JWT generic secure usage in the following series of posts:

• Stand Up for JWT Revocation
• JWT Revocation Strategies
• JWT Secure Usage
• A secure JWT authentication implementation for Rack and Rails

devise-jwt is just a thin layer on top of warden-jwt_auth that configures it to be used out of the box with devise and Rails.

Installation

Add this line to your application's Gemfile:

gem 'devise-jwt', '~> 0.5.2'

And then execute:

$ bundle

Or install it yourself as:

$ gem install devise-jwt

Usage

First you need to configure devise to work in an API application. You can follow the instructions in this project wiki page Configuring devise for APIs (you are more than welcome to improve them).

Secret key configuration

First of all, you have to configure the secret key that will be used to sign generated tokens. You can do it in the devise initializer:

Devise.setup do |config|
  # ...
  config.jwt do |jwt|
    jwt.secret = ENV['DEVISE_JWT_SECRET_KEY']
  end
end

Important: You are encouraged to use a secret different than your application secret_key_base. It is quite possible that some other component of your system is already using it. If several components share the same secret key, chances that a vulnerability in one of them has a wider impact increase. In rails, generating new secrets is as easy as bundle exec rake secret. Also, never share your secrets pushing it to a remote repository, you are better off using an environment variable like in the example.

Currently, HS256 algorithm is the one in use.

Model configuration

You have to tell which user models you want to be able to authenticate with JWT tokens. For them, the authentication process will be like this:

• A user authenticates through devise create session request (for example, using the standard :database_authenticatable module).
• If the authentication succeeds, a JWT token is dispatched to the client in the Authorization response header, with format Bearer #{token} (tokens are also dispatched on a successful sign up).
• The client can use this token to authenticate following requests for the same user, providing it in the Authorization request header, also with format Bearer #{token}
• When the client visits devise destroy session request, the token is revoked.

See request_formats configuration option if you are using paths with a format segment (like .json) in order to use it properly.

As you see, unlike other JWT authentication libraries, it is expected that tokens will be revoked by the server. I wrote about why I think JWT revocation is needed and useful.

An example configuration:

class User < ApplicationRecord
  devise :database_authenticatable,
         :jwt_authenticatable, jwt_revocation_strategy: Blacklist
end

If you need to add something to the JWT payload, you can do it defining a jwt_payload method in the user model. It must return a Hash. For instance:

def jwt_payload
  { 'foo' => 'bar' }
end

You can add a hook method on_jwt_dispatch on the user model. It is executed when a token dispatched for that user instance, and it takes token and payload as parameters.

def on_jwt_dispatch(token, payload)
  do_something(token, payload)
end

Note: if you are making cross-domain requests, make sure that you add Authorization header to the list of allowed request headers and exposed response headers. You can use something like rack-cors for that, for example:

config.middleware.insert_before 0, Rack::Cors do
  allow do
    origins 'http://your.frontend.domain.com'
    resource '/api/*',
      headers: %w(Authorization),
      methods: :any,
      expose: %w(Authorization),
      max_age: 600
  end
end

Revocation strategies

devise-jwt comes with three revocation strategies out of the box. Some of them are implementations of what is discussed in the blog post JWT Revocation Strategies, where I also talk about their pros and cons.

JTIMatcher

Here, the model class acts itself as the revocation strategy. It needs a new string column with name jti to be added to the user. jti stands for JWT ID, and it is a standard claim meant to uniquely identify a token.

It works like the following:

• At the same time that a token is dispatched for a user, the jti claim is persisted to the jti column.
• At every authenticated action, the incoming token jti claim is matched against the jti column for that user. The authentication only succeeds if they are the same.
• When the user requests to sign out its jti column changes, so that provided token won't be valid anymore.

In order to use it, you need to add the jti column to the user model. So, you have to set something like the following in a migration:

def change
  add_column :users, :jti, :string, null: false
  add_index :users, :jti, unique: true
  # If you already have user records, you will need to initialize its `jti` column before setting it to not nullable. Your migration will look this way:
  # add_column :users, :jti, :string
  # User.all.each { |user| user.update_column(:jti, SecureRandom.uuid) }
  # change_column_null :users, :jti, false
  # add_index :users, :jti, unique: true
end

Important: You are encouraged to set a unique index in the jti column. This way we can be sure at the database level that there aren't two valid tokens with same jti at the same time.

Then, you have to add the strategy to the model class and configure it accordingly:

class User < ApplicationRecord
  include Devise::JWT::RevocationStrategies::JTIMatcher
  
  devise :database_authenticatable,
         :jwt_authenticatable, jwt_revocation_strategy: self
end

Be aware that this strategy makes uses of jwt_payload method in the user model, so if you need to use it don't forget to call super:

def jwt_payload
  super.merge('foo' => 'bar')
end

Blacklist

In this strategy, a database table is used as a blacklist of revoked JWT tokens. The jti claim, which uniquely identifies a token, is persisted. The exp claim is also stored to allow the clean-up of staled tokens.

In order to use it, you need to create the blacklist table in a migration:

def change
  create_table :jwt_blacklist do |t|
    t.string :jti, null: false
    t.datetime :exp, null: false
  end
  add_index :jwt_blacklist, :jti
end

For performance reasons, it is better if the jti column is an index.

Note: if you used the blacklist strategy before vesion 0.4.0 you may not have the field exp. If not, run the following migration:

class AddExpirationTimeToJWTBlacklist < ActiveRecord::Migration
  def change
    add_column :jwt_blacklist, :exp, :datetime, null: false
  end
end

Then, you need to create the corresponding model and include the strategy:

class JWTBlacklist < ApplicationRecord
  include Devise::JWT::RevocationStrategies::Blacklist

  self.table_name = 'jwt_blacklist'
end

Last, configure the user model to use it:

class User < ApplicationRecord
  devise :database_authenticatable,
         :jwt_authenticatable, jwt_revocation_strategy: JWTBlacklist
end

Whitelist

Here, the model itself acts also as a revocation strategy, but it needs to have a one-to-many association with another table which stores the tokens (in fact their jti claim, which uniquely identifies them) valids for each user record.

The workflow is as the following:

• Once a token is dispatched for a user, its jti claim is stored in the associated table.
• At every authentication, the incoming token jti is matched against all the jti associated to that user. The authentication only succeeds if one of them matches.
• On a sign out, the token jti is deleted from the associated table.

In fact, besides the jti claim, the aud claim is also stored and matched at every authentication. This, together with the aud_header configuration parameter, can be used to differentiate between clients or devices for the same user.

The exp claim is also stored to allow the clean-up of staled tokens.

In order to use it, you have to create yourself the associated table and model. The association table must be called whitelisted_jwts:

def change
  create_table :whitelisted_jwts do |t|
    t.string :jti, null: false
    t.string :aud
    # If you want to leverage the `aud` claim, add to it a `NOT NULL` constraint:
    # t.string :aud, null: false
    t.datetime :exp, null: false
    t.references :your_user_table, foreign_key: true
  end
  
  add_index :whitelisted_jwts, :jti, unique: true
end

Important: You are encouraged to set a unique index in the jti column. This way we can be sure at the database level that there aren't two valid tokens with same jti at the same time.

And then, the model:

class WhitelistedJwt < ApplicationRecord
end

Finally, include de strategy in the model and configure it:

class User < ApplicationRecord
  include Devise::JWT::RevocationStrategies::Whitelist
  
  devise :database_authenticatable,
         :jwt_authenticatable, jwt_revocation_strategy: self
end

Be aware that this strategy makes uses of on_jwt_dispatch method in the user model, so if you need to use it don't forget to call super:

def on_jwt_dispatch(token, payload)
  super
  do_something(token, payload)
end

Null strategy

A null object pattern strategy, which does not revoke tokens, is provided out of the box just in case you are absolutely sure you don't need token revocation. It is recommended not to use it.

class User < ApplicationRecord
  devise :database_authenticatable,
         :jwt_authenticatable, jwt_revocation_strategy: Devise::JWT::RevocationStrategies::Null
end

Custom strategies

You can also implement your own strategies. They just need to implement two methods: jwt_revoked? and revoke_jwt, both of them accepting as parameters the JWT payload and the user record, in this order.

For instance:

module MyCustomStrategy
  def self.jwt_revoked?(payload, user)
    # Does something to check whether the JWT token is revoked for given user
  end
  
  def self.revoke_jwt(payload, user)
    # Does something to revoke the JWT token for given user
  end
end

class User < ApplicationRecord
  devise :database_authenticatable,
         :jwt_authenticatable, jwt_revocation_strategy: MyCustomStrategy
end

Testing

Models configured with :jwt_authenticatable can't be retrieved from the session. For this reason, sign_in devise testing helper methods won't work as expected.

What you need to do in order to authenticate test environment requests is the same that you will do in production: to provide a valid token in the Authorization header (in the form of Bearer #{token}) at every request.

There are two ways you can get a valid token:

• Inspecting the Authorization response header after a valid sign in request.
• Manually creating it.

The first option tests the real workflow of your application, but it can slow things if you perform it at every test.

For the second option, a test helper is provided in order to add the Authorization name/value pair to given request headers. You can use it as in the following example:

# First, require the helper module
require 'devise/jwt/test_helpers'

# ...

  it 'tests something' do
    user = fetch_my_user()
    headers = { 'Accept' => 'application/json', 'Content-Type' => 'application/json' }
    # This will add a valid token for `user` in the `Authorization` header
    auth_headers = Devise::JWT::TestHelpers.auth_headers(headers, user)
    
    get '/my/end_point', headers: auth_headers
    
    expect_something()
  end

Usually you will wrap this in your own test helper.

Configuration reference

This library can be configured calling jwt on devise config object:

Devise.setup do |config|
  config.jwt do |jwt|
    # ...
  end
end

secret

Secret key used to sign generated JWT tokens. You must set it.

expiration_time

Number of seconds while a JWT is valid after its generation. After that, it won't be valid anymore, even if it hasn't been revoked.

Defaults to 3600 (1 hour).

dispatch_requests

Besides the create session one, additional requests where JWT tokens should be dispatched.

It must be a bidimensional array, each item being an array of two elements: the request method and a regular expression that must match the request path.

For example:

jwt.dispatch_requests = [
                          ['POST', %r{^/dispatch_path_1$}],
                          ['GET', %r{^/dispatch_path_2$}],
                        ]

Important: You are encouraged to delimit your regular expression with ^ and $ to avoid unintentional matches.

revocation_requests

Besides the destroy session one, additional requests where JWT tokens should be revoked.

It must be a bidimensional array, each item being an array of two elements: the request method and a regular expression that must match the request path.

For example:

jwt.revocation_requests = [
                            ['DELETE', %r{^/revocation_path_1$}],
                            ['GET', %r{^/revocation_path_2$}],
                          ]

Important: You are encouraged to delimit your regular expression with ^ and $ to avoid unintentional matches.

request_formats

Request formats that must be processed (in order to dispatch or revoke tokens).

It must be a hash of devise scopes as keys and an array of request formats as values. When a scope is not present or if it has a nil item, requests without format will be taken into account.

For example, with following configuration, user scope would dispatch and revoke tokens in json requests (as in /users/sign_in.json), while admin_user would do it in xml and with no format (as in /admin_user/sign_in.xml and /admin_user/sign_in).

jwt.request_formats = {
                        user: [:json],
                        admin_user: [nil, :xml]
                      }

By default, only requests without format are processed.

aud_header

Request header which content will be stored to the aud claim in the payload.

It is used to validate whether an incoming token was originally issued to the same client, checking if aud and the aud_header header value match. If you don't want to differentiate between clients, you don't need to provide that header.

Important: Be aware that this workflow is not bullet proof. In some scenarios a user can handcraft the request headers, therefore being able to impersonate any client. In such cases you could need something more robust, like an OAuth workflow with client id and client secret.

Defaults to JWT_AUD.

Development

There are docker and docker-compose files configured to create a development environment for this gem. So, if you use Docker you only need to run:

docker-compose up -d

An then, for example:

docker-compose exec app rspec

This gem uses overcommit to execute some code review engines. If you submit a pull request, it will be executed in the CI process. In order to set it up, you need to do:

bundle install --gemfile=.overcommit_gems.rb
overcommit --sign
overcommit --run # To test if it works

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/waiting-for-dev/devise-jwt. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

Release Policy

devise-jwt follows the principles of semantic versioning.

License

The gem is available as open source under the terms of the MIT License.