In general, it feels more "natural" to a user to click on the browser back button and end up back to a previous node in a tree. It's best to give users the ability to go back in a tree at any moment.
An example: users type their email address and need to validate it. Ideally, users should have the ability to go back and verify the address they typed if for example they didn't receive the validation link (mistyped).
Currently, when the back button is clicked, the redirection takes to the previous page. However this may need changing if the authN process updates the UI through JS-based callbacks and this is a common problem with single-page applications (if we can consider the authentication process a sort of a SPA). If the authN process updates the UI without changing the browser URL, it is normal to redirect the user to the previous page upon pressing the back button.
Also, it could be that a "verify my address" outcome could be added and change the input collector node to pre-fill the field with the email that the user typed previously.