def credentials(credentials_override = nil)
      result = super(credentials_override)
      validate_headers_for_server(result)

      extra_headers = {
        'userAgent' => generate_user_agent(),
        'developerToken' => result[:developer_token]
      }
      extra_headers['clientCustomerId'] = result[:client_customer_id] if
          result[:client_customer_id]
      extra_headers['validateOnly'] = 'true' if @validate_only
      extra_headers['partialFailure'] = 'true' if @partial_failure
      result[:extra_headers] = extra_headers
      return result
    end
def credentials(credentials_override = nil)
      result = super(credentials_override)
      validate_headers_for_server(result)

      extra_headers = {
        'userAgent' => generate_user_agent(),
        'developerToken' => result[:developer_token]
      }
      extra_headers['clientCustomerId'] = result[:client_customer_id] if
          result[:client_customer_id]
      extra_headers['validateOnly'] = 'true' if @validate_only
      extra_headers['partialFailure'] = 'true' if @partial_failure
      result[:extra_headers] = extra_headers
      return result
    end
Create the list of credentials to be used by the auth handler for header
 generation.