I have a backend contact form with a backend success page; after submitting the form,
there is a (backend) redirect to that success page.
The form I have is not a “login form” or an “order form” so there is no sensitive data such as passwords or billing details (as well as billing as an action) involved; thus there isn’t really a problem if a user goes “back” in the browser, but still, in principle, what can be done to prevent users from going back to a backend form, FROM a backend success page? Asking from mere curiosity (there is no problem to solve here, just curiosity about such backend situations which today are quite rare due to AJAX).
99 percent of users who fill out forms are only going to do it once and only because they have to or want something to happen. That’s why if a form is long or overly complicated they will simply move on to a website that is easier to use. That being said I highly doubt that they are going to back to the form or to the success page unless they are a developer which would be more of a compliment in my opinion.