It woudl be great if extended patron attributes could be mapped for provisioning with Shibboleth as well. One use case would be a unique key, that is also used/neded for patron imports and stored in an unique extended patron attribute.
This is taken care of in bug 39224 where I expose the mapping option (for all supported IdP types) in the updated admin UI. *** This bug has been marked as a duplicate of bug 39224 ***