Apple no longer needs your password for your User account for any hardware repairs.
Apple runs diagnostics via NetBoot to ensure the repair is successful.
You should always have a backup of your data and if you have any concern about someone snooping around your files during a repair, then create another User (Admin) account and delete yours.
The only time Apple will ask for your password is when they are performing a data migration or trying to fix a software issue. We don’t have the time nor the inclination to look at your files in the first place. Has it happened before??? Yes… and those Genius staff were fired. I always explain to my customers that their info isn’t worth losing my job over.