How to use devise-jwt with devise for signin, sign

I am using rails for the backend using devise-jwt and react for the frontend part.

I am following this https://github.com/waiting-for-dev/devise-jwt/blob/master/README.md

my routes.rb file contains:

 Rails.application.routes.draw do
  # remove this in production
  require 'sidekiq/web'
  mount Sidekiq::Web => '/sidekiq'

  namespace :api, defaults: { format: 'json' } do
    namespace :v1 do
      devise_for :users, :controllers => {sessions: 'api/v1/sessions', registrations: 'api/v1/registrations'}
    end
  end
end

my registrations_controller.rb (app/controllers/api/registrations_controller.rb)

class Api::V1::RegistrationsController < Devise::RegistrationsController
  respond_to :json, :controllers => {sessions: 'sessions', registrations: 'registrations'}

  before_action :sign_up_params, if: :devise_controller?, on: [:create]

  def create
    build_resource(sign_up_params)

    if resource.save
      render :json => resource, serializer: Api::V1::UserSerializer, meta: { message: 'Sign up success', token: request.headers["Authorization"] }, :status => :created
    else
      render :json => resource, adapter: :json_api, serializer: ActiveModel::Serializer::ErrorSerializer, meta: { message: 'Sign up success' }, :status => :created
    end
  end


  protected

  def sign_up_params
    params.require(:sign_up).permit(:first_name, :last_name, :mobile, :email, :password, :password_confirmation)
  end
end

my sessions_controller.rb (app/controllers/api/sessions_controller.rb)

class Api::SessionsController < Devise::SessionsController  
  respond_to :json
end

my application_controller.rb (app/controllers/application_controller.rb)

class ApplicationController < ActionController::Base
end

Basically what will be the next step to acees the token. I am confused. How will i get the acess token and use it to authenticate in the frontend react part.

Assuming you have your server-side setup the response will include an Authorization Header.

On the front-end you'll make request to sign in and have a callback to catch the response:

 window.fetch(LOGIN_URL, dataWithLoginInfo).then(response => {
    const jwt = response.headers.get('Authorization').split('Bearer ')[1];
    window.sessionStorage.setItem('jwt', jwt);
  }).catch(handleError)

Next make the requests with the Authorization header included:

const token =  window.sessionStorage.getItem('jwt')
const headers = { Authorization: `Bearer ${token}` }

or use it in your app after you decode it:

import jwt from 'jsonwebtoken';
const decodedToken = jwt.decode(window.sessionStorage.getItem('jwt'));

if (decodedToken.isAdmin) {
  return <AdminPage />;
} else {
  return <NotAdminPage />;
}

You'll use something like https://www.npmjs.com/package/jwt-decode or https://www.npmjs.com/package/jsonwebtoken to decode the token and read the information from it like id, roles, permissions, etc.

You really need to follow a tutorial like: https://auth0.com/blog/secure-your-react-and-redux-app-with-jwt-authentication/ or http://jasonwatmore.com/post/2017/12/07/react-redux-jwt-authentication-tutorial-example. Then have some local expert take a look at all your code.