Is it possible to use drush migrate-import to import custom fields? I am trying to migrate a Drupal 7 site to Drupal 8 on a new server
I have copied the db so it can be used locally. 
I have run the drush migrate command and migrate-status shows a bunch of things that are ready for import. 
I can import users with drush migrate-import d7_upgrade_users. However the users have custom fields associated with them and I can't find how to import those fields through drush. 
Trying to export a csv from the old host is virtually impossible as it crashes out trying to do the export. 

Is it possible to import all user data including passwords and custom fields from the command line using drush (or other command line tools) without the need to import everything?
I am currently working on a similar migration and had a similar problem. In my case the custom fields were part of the Profile2 module in D7. I installed the D8 Profile module and added a patch that fixes the Profile2 import

https://www.drupal.org/files/issues/2018-05-16/profile-migrate-from-profile2-D8-2957256-4.patch

After that, the custom fields were automatically created, populated and linked to the correct user.

Not sure if that is what you need.