Redirect based on text entry answer

I have a somewhat complicated attention check that I'm not sure how to build and am hoping someone can help me with.
My survey has 4 different conditions, with a randomizer branching to present participants with one of four different stimuli at the very beginning (I'm saving their condition as an embedded variable). Then on the next page one of the things I have is a text entry question where the correct answer will depend on which condition they were in. So in essence what I have to do is convert their text entry answer to fully lowercase (because we don't consider the answer case sensitive), then check whether it equals some condition-dependent string, and if it doesn't then redirect them to a termination url (letting them continue in the survey if their answer was correct).
Does anyone know how I can do something like this?
Thanks in advance!