For a puzzle game I'm currently searching for a way to redirect depending on a text input.

Quick example: Player finds code 23eq, enters this on the website and then gets to another page with another part of the story (or hint, puzzle etc.). If he/she enters a wrong code, it's denied (possibly by modified 404-page).

My idea of implementation: forwarding while adding string [input value] to url. But sadly, I'm more a frontend / html / css guy than php / js.

Any ideas? Thank you very much!