There are some pages, like aws, which are designed to be multitenant, you have to enter an account with the username/password as well.
You might have the same username on different accounts, the problem is that you can't keep multiple instances of user/password for the same user and page.
If you could append a comment at the end of the username after some char (I.a #) then you could store the same user, with different passwords, and when you log in you choose one, and the comment section of the username should not be entered on the username form field.
I already do that manually, having to remove manually the comment from the field after choosing it from the list.
Thanks and kind regards.