An important thing to know is that our sessions (for admin apps) last for 20 hours, which is good because that means this will never delete sessions which are in use. That 20 hours (default) is defined over here: https://github.com/alphagov/gds-sso/blob/95f09e01b435c32a524a39ad56fa89eae364c762/lib/gds-sso/config.rb#L19