Example module to perform remote authentication with Devise

remote_authenticatable.rb

module Devise
  module Models
    module RemoteAuthenticatable
      extend ActiveSupport::Concern

      #
      # Here you do the request to the external webservice
      #
      # If the authentication is successful you should return
      # a resource instance
      #
      # If the authentication fails you should return false
      #
      def remote_authentication(authentication_hash)
        # Your logic to authenticate with the external webservice
      end

      module ClassMethods
        ####################################
        # Overriden methods from Devise::Models::Authenticatable
        ####################################

        #
        # This method is called from:
        # Warden::SessionSerializer in devise
        #
        # It takes as many params as elements had the array
        # returned in serialize_into_session
        #
        # Recreates a resource from session data
        #
        def serialize_from_session(id)
          resource = self.new
          resource.id = id
          resource
        end

        #
        # Here you have to return and array with the data of your resource
        # that you want to serialize into the session
        #
        # You might want to include some authentication data
        #
        def serialize_into_session(record)
          [record.id]
        end

      end
    end
  end
end