Question

I’m writing a PHP app which presents people with a form to fill out and submit.

Once the user submits the form, things change in the database and the form should become inaccessible to the user.

If, however, the user presses the back button after submitting the form, they can see it again. I have code in the back end to prevent a user from being able to re-submit an already submitted form, however ideally if the user presses the back button, they will get the same message as if they were to just navigate to it outright: A message is shown on the screen saying that this form has already been submitted and is now unavailable.

Aside from an AJAX call to the back-end to check if the form has already been submitted, and redirect the user to the “form submitted and now unavailable” message, is there any other (better?) way of handling this?

Since this will only be used internally on a SOE, I only need it to work on IE8+.

Answer 1

You can consider adding this information to session/cookie. Alternatively if you have authentication system, you can store this information in the database.
Probably the first option is easier and sufficient.

so basically before displaying the form you check if the cookie alreadySubmitted is 1. If yes – error message, otherwise – form. When you submit the form, just set this cookie to alreadySubmitted.

However be aware, that if someone deletes cookie, he will be able to trick your system.