Sliding objects along colliding walls

MoveCube.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class MoveCube : MonoBehaviour {
	private Rigidbody rb;
	private Dictionary<GameObject, Vector3> walls = new Dictionary<GameObject, Vector3>();

	void OnCollisionEnter(Collision other) {
		walls.Add(other.gameObject, other.contacts[0].normal);
	}

	void OnCollisionExit(Collision other) {
		walls.Remove(other.gameObject);
	}

	void Start() {
		rb = GetComponent<Rigidbody>();
	}
	
	void Update () {
		// Replace this with your input code
		Vector3 movement = new Vector3(5, rb.velocity.y, -5f);

		foreach (var w in walls) {
			if (Vector3.Angle(movement, w.Value) > 90) {
				movement = Vector3.ProjectOnPlane(movement, w.Value);
			}
		}
		
		rb.velocity = movement;
	}
}