def soap_header_handler(auth_handler, version, header_ns, default_ns)
      auth_method = @config.read('authentication.method', :OAUTH2)
      handler_class = case auth_method
        when :OAUTH2, :OAUTH2_SERVICE_ACCOUNT
          AdsCommon::SavonHeaders::OAuthHeaderHandler
        else
          raise AdsCommon::Errors::AuthError,
              "Unknown auth method: %s" % auth_method
        end
      return handler_class.new(@credential_handler, auth_handler, header_ns,
                                  default_ns, version)
    end
def soap_header_handler(auth_handler, version, header_ns, default_ns)
      auth_method = @config.read('authentication.method', :OAUTH2)
      handler_class = case auth_method
        when :OAUTH2, :OAUTH2_SERVICE_ACCOUNT
          AdsCommon::SavonHeaders::OAuthHeaderHandler
        else
          raise AdsCommon::Errors::AuthError,
              "Unknown auth method: %s" % auth_method
        end
      return handler_class.new(@credential_handler, auth_handler, header_ns,
                                  default_ns, version)
    end
Retrieve correct soap_header_handler.

 Args:
 - auth_handler: instance of an AdsCommon::Auth::BaseHandler subclass to
   handle authentication
 - version: intended API version
 - header_ns: header namespace
 - default_ns: default namespace

 Returns:
 - SOAP header handler