Symptoms
The following error is displayed when a website is imported in Domains > example.com > Website Importing:

Migrating from cPanel via Tools & Settings > Migration & Transfer Manager fails with the following error:
Failed to perform action: Fetch data from source cPanel
Cause: Failed to connect to the the source server 'cpanel' (203.0.113.2) at '203.0.113.2' by SSH as 'root': ('Bad authentication type', [u'publickey', u'gssapi-keyex', u'gssapi-with-mic']) (allowed_types=[u'publickey', u'gssapi-keyex', u'gssapi-with-mic'])
That is a critical error, migration was stopped.
Cause
Password authentication is disabled on the source server.
Note: In regards to Website Importing the warning also appears if the SSH access on the source server was configured via SSH key only.
Resolution
Connect to the source server via SSH
Edit file
/etc/ssh/sshd_configand enable SSH authentication by password:PasswordAuthentication yes
Import website via Domains > example.com > Website Importing or via Tools and Settings > Migration & Transfer Manager by specifying the SSH username and password.