Adding SSO after many users already signed up -- how to migrate them?

Product Support SSO
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root@server:~# cd /var/discourse/
root@server:/var/discourse# ./launcher enter app
x86_64 arch detected.
root@server:/var/www/discourse# rails c
[1] pry(main)> Rails.configuration.pbkdf2_iterations
=> 64000
[2] pry(main)>