View the original community article here
Last tested: Jul 6, 2020
SAML has a predefined notion of a ‘nameid’ in the saml response document. We use that as the unique id for looker users. If you are not changing that per user, then all is good.
If you are changing that, then you'll have to use the API to add credentials_email to all of the existing users that have the email of the new domain. Then when you move to the new domain, select the "merge users by email" option and it should be okay.
Note: A colleague made an extension to help with this:
Please note this is not officially supported resource - if you have a migration situation, please reach out by filling an Issue in the git repo to get some help through it!