code: def create_auth_handler()
        auth_method = @config.read('authentication.method', :OAUTH2)
        return case auth_method
          when :OAUTH
            raise AdsCommon::Errors::Error,
                'OAuth authorization method is deprecated, use OAuth2 instead.'
          when :OAUTH2
            AdsCommon::Auth::OAuth2Handler.new(
                @config,
                api_config.config(:oauth_scope)
            )
          when :OAUTH2_SERVICE_ACCOUNT
            AdsCommon::Auth::OAuth2ServiceAccountHandler.new(
                @config,
                api_config.config(:oauth_scope)
            )
          else
            raise AdsCommon::Errors::Error,
                "Unknown authentication method '%s'" % auth_method
          end
      end
docs: Auxiliary method to create an authentication handler.
  
   Returns:
   - auth handler