Changes you need to make in order to make Devise use JWT Header Authentication

devise.rb

# Add somewhere to your Devise configuration
# "config/initializers/devise.rb"

Devise.setup do |config|
  # ...

  config.warden do |manager|
    # Registering your new Strategy
    manager.strategies.add(:jwt, Devise::Strategies::JsonWebToken)

    # Adding the new JWT Strategy to the top of Warden's list,
    # Scoped by what Devise would scope (typically :user)
    manager.default_strategies(scope: :user).unshift :jwt
  end
  
  # ...
end

Gemfile

# Add the "https://github.com/jwt/ruby-jwt" gem to your "Gemfile"
gem 'jwt'

index.html.erb

# Add the following code to a view
# It will show you an example of how to make a
# curl HTTP request with the proper authentication headers.
# Be sure to actually use a working route and not "http://localhost:3000/api/v1/yada_yada"

<% if user_signed_in? %>
  curl -X GET --header 'Authorization: Bearer <%= JWTWrapper.encode({ user_id: current_user.id }) %>' 'http://localhost:3000/api/v1/yada_yada'
<% end %>

json_web_token.rb

# Your actual JWT Strategy
# "config/initializers/core_extensions/devise/strategies/json_web_token.rb"

module Devise
  module Strategies
    class JsonWebToken < Base
      def valid?
        request.headers['Authorization'].present?
      end

      def authenticate!
        return fail! unless claims
        return fail! unless claims.has_key?('user_id')

        success! User.find_by_id claims['user_id']
      end

      protected ######################## PROTECTED #############################

      def claims
        strategy, token = request.headers['Authorization'].split(' ')

        return nil if (strategy || '').downcase != 'bearer'

        JWTWrapper.decode(token) rescue nil
      end
    end
  end
end

jwt_wrapper.rb

# Helper module for you to use on your app and in your Strategy
# Don't add "Helper" to its name and rails won't load it has a view helper module.
# "app/helpers/jwt_wrapper.rb"

module JWTWrapper
  extend self

  def encode(payload, expiration = nil)
    expiration ||= Rails.application.secrets.jwt_expiration_hours

    payload = payload.dup
    payload['exp'] = expiration.to_i.hours.from_now.to_i

    JWT.encode payload, Rails.application.secrets.jwt_secret
  end

  def decode(token)
    begin
      decoded_token = JWT.decode token, Rails.application.secrets.jwt_secret

      decoded_token.first
    rescue
      nil
    end
  end
end

secrets.yml

# Add somewhere to your secrets yml
# "config/secrets.yml"

development:
  # ...
  jwt_secret: 'super random key'
  jwt_expiration_hours: 24
  # ...

production:
  # ...
  jwt_secret: 'even more super random key'
  jwt_expiration_hours: 6
  # ...