How do I migrate user passwords? I have refactored an old Drupal 6 site to Drupal 8 and my only problem is, i migrated the users but the password is incorrect. i know that the password in Drupal 6 is a MD5 hash, but i cannot find a solution to convert this password, that Drupal 8 can read it. 

Is there any solution for the password migration yet? can i give the MD5 hash a prefix inside of the database to make it readable?
Security wise it would make sense to import them in Drupal and then use the Mass Password Reset module to reset all passwords.