So first we will create rails project and setup device

create a rails application

rails new devise_example

now add devise to gem list

you can find a file named 'Gemfile' at the root of rails project

Then run bundle install

Next, you need to run the generator:

rails generate devise:install

Now on console you can find few instructions just follow it.

Generate devise model

rails generate devise MODEL

Then run rake db:migrate

For more details go to: Devise Gem

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Authentication Token

Authentication token is used to authenticate a user with a unique token, So Before we proceed with the logic first we need to add auth_token field to a Devise model

Hence,

rails g migration add_authentication_token_to_users

class AddAuthenticationTokenToUsers < ActiveRecord::Migration
  def change
    add_column :users, :auth_token, :string, default: ""
    add_index :users, :auth_token, unique: true
  end
end

Then run rake db:migrate

Now we are all set to do authentication using auth_token

In app/controllers/application_controllers.rb

First this line to it

respond_to :html, :json 

this will help rails application respond with both html and json

Then

protect_from_forgery with: :null

will change this :null as we are not dealing with sessions.

now we will add authentication method in application_controller

So, by default Devise uses email as unique field we can also use custom fields, for this case we will be authenticating using user_email and auth_token.

  before_filter do
    user_email = params[:user_email].presence
    user       = user_email && User.find_by_email(user_email)

    if user && Devise.secure_compare(user.authentication_token, params[:auth_token])
      sign_in user, store: false
    end
  end

Note: Above code is purely based on your logic i am just trying to explain the working example

On line 6 in the above code you can see that i have set store: false which will prevent from creating a session on each requests hence we achieved stateless re