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JWT is a Json Web Token, it is a standard and has been implemented in almost all popular programming languages. Hence, they can be easily used or exchanged in systems implemented in diverse platforms.

JWT has libraries for almost all platforms and Ruby is no exception.

Now we will see how JWT is used in Rails:

We will create a simple Rails application which uses the excellent Devise gem for authentication and the jwt gem for creating and verifying JWT tokens.

Let’s create a sample Rails application:

rails new rails_on_jwt

Once the application is generated, create a Home controller which we will use to check our authentication.

Create  home_controller.rb in the app/controllers

classHomeController ApplicationController
	def index
	end
end

Write the route for  HomeController to /home in config/routes.rb:

Rails.application.routes.draw do
get 'home' => 'home#index'
end

Now, add Devise to our application. First, we will add the Devise and jwt gems in our Gemfile.

gem 'devise'
gem 'jwt'

Then run a command “bundle install” on terminal.

Now let’s create the Devise configuration files:

For that we have will have to create the Devise User model and migrate the database:

rails g devise User
rakedb:migrate

Created User Model use for authentication.now  It’s time to integrate jwt into our application. First, we will create a class named JsonWebToken in lib/json_web_token.rb.This class will encapsulate the JWT token encoding and decoding logic.

classJsonWebToken
defself.encode(payload)
JWT.encode(payload, Rails.application.secrets.secret_key_base)
end

defself.decode(token)
returnHashWithIndifferentAccess.new(JWT.decode(token, Rails.application.secrets.secret_key_base)[0])
rescue
nil
end
end

We have to create an initializer for including the JsonWebToken class in config/initializers/jwt.rb.

require 'json_web_token'

We have to add some helper method in ApplicationController class which we will use in AuthenticationController class:

In app/controllers/application_controller.rb:

classApplicationController
<ActionController::Base
attr_reader :current_user

protected
defauthenticate_request!
unlessuser_id_in_token?
renderjson: { errors: ['Not Authenticated'] }, status: :unauthorized
return
end
    @current_user = User.find(auth_token[:user_id])
rescue JWT::VerificationError, JWT::DecodeError
renderjson: { errors: ['Not Authenticated'] }, status: :unauthorized
end

private
defhttp_token
      @http_token ||= if request.headers['Authorization'].present?
request.headers['Authorization'].split(' ').last
end
end

defauth_token
    @auth_token ||= JsonWebToken.decode(http_token)
end

defuser_id_in_token?
http_token&&auth_token&&auth_token[:user_id].to_i
end
end 

We have added a few helper methods like authenticate_request!which will act as a before_filter to check user credentials and we have created AuthenticationController to handle all authentication requests to the API. In app/controllers/authentication_controller.rb:

classAuthenticationController<ApplicationController
defauthenticate_user
user = User.find_for_database_authentication(email: params[:email])
ifuser.valid_password?(params[:password])
renderjson: payload(user)
else
renderjson: {errors: ['Invalid Username/Password']}, status: :unauthorized
end
end
private
def payload(user)
return nil unless user and user.id
    {
auth_token: JsonWebToken.encode({user_id: user.id}),
user: {id: user.id, email: user.email}
    }
end
end

Here we have added AuthenticationController to implement the authentication endpoint. It uses Devise to authenticate the user and issue a JWT if the credentials are valid.

Now we have to update our routes.rb to add the authentication endpoint.

Rails.application.routes.draw do
post 'auth_user' => 'authentication#authenticate_user'
get 'home' => 'home#index'
end

Also, we have to modify the HomeController to secure it using a before_filter and add a meaningful response in case of successful authentication:

classHomeController<ApplicationController
before_filter :authenticate_request!
def index
renderjson: {'logged_in' => true}
	end
end

Now, create a sample user to test the authentication by using rails console or by Using Seed command:Start the server and check out how JWT authentication works:

rails s