Move Along Spline with Input

Hello, I’m trying to make a 2.5D game and I have an issue making a path climbing along spline.
Basically when I interact with a path I get the spline and change the movement type (to fly or custom tbh right now I got no idea which one) and then with my inputs WASD i need to be able to move along the spline only.
I’ve seen people using timeline and lerp but that’s not a thing since I need to move along it but only with input and also the same speed it would have, I would see that as an option if I had to just keep a button pressed to make it go forward on it or backwards on it but I need full control.
Have no idea, also I would appreciate new ideas if there are better ways to make a scripted movement with inputs.

" I would see that as an option if I had to just keep a button pressed to make it go forward on it or backwards on it but I need full control."

what does this full control mean?

Sorry for writing only now, basically what I was trying was to move along a spline following it with WASD, but more of a “real movement”, so what I mean is that mostly I’ve seen people using lerp so that you press W you go to the next spline point and S the previous but I had to actually move the player with WASD, like imagine you have a climbable leaf path on a wall you want to move on it following that with WASD based on the path you have to follow, that wasnt my case because splines werent needed for that, but in my case it is so i was searching a way to do it, in the end i found a way with some advanced mats, dot products etc… chatgpt helped me there