"Cutting corners" means doing something more easily or quickly than you're supposed to. For example, if you're a cleaner who doesn't want to work hard, you might "cut corners" by only cleaning the areas that look dirty.
This phrase has a negative association. We think of "cutting corners" as lazy or dishonest.
You can use "on" and "by" with the phrase like this:
A lot of employees cut corners on security by sharing or re-using passwords.