Import soap webservice xml to node with Feeds?
I assume you have no access to change the feed provider.

There are couple of additional contributed modules which handle different types of authentication for the feeds module.

This handles regular http authentication, which is more likely with soap:
https://www.drupal.org/project/feeds_httpfetcher_aa

and this one is for oauth which ia also possible with soap:
https://www.drupal.org/project/feeds_oauth