You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: session_refresher.rb
    path of file: ./repos/vets-api/app/services/sign_in
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module SignIn
  class SessionRefresher
    attr_reader :refresh_token, :anti_csrf_token, :session

    def initializ
    
    def perform
      find_valid_oauth_session
      validate_credential_lock
      validate_terms_of_use if client_config.enforced_terms.present?
      anti_csrf_check if anti_csrf_enabled_client?
      detect_token_theft
      update_session! if parent_refresh_token_in_session?
      create_new_tokens
    end