How to rotate object with the keys A/D?

I have a code to move the object up/down/let/right. But what if I want ro rotate it left/right with the keys A/D, not move?

using UnityEngine;
using System.Collections;

public class MoveSphere : MonoBehaviour {

	public GameObject player;
	public int speed = 5;

	void Start ()
	{
		player = (GameObject)this.gameObject;
	}

	void Update ()
	{
		if 		(Input.GetKey(KeyCode.W) || Input.GetKey(KeyCode.UpArrow)) 
			player.transform.position += player.transform.forward * speed * Time.deltaTime; 
		
		else if (Input.GetKey(KeyCode.S) || Input.GetKey(KeyCode.DownArrow)) 
			player.transform.position -= player.transform.forward * speed * Time.deltaTime;
		
		else if (Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.LeftArrow)) 
			player.transform.position -= player.transform.right * speed * Time.deltaTime;
		
		else if (Input.GetKey(KeyCode.D) || Input.GetKey(KeyCode.RightArrow))
			player.transform.position += player.transform.right * speed * Time.deltaTime;
	}
}

this could also work transform.Rotate(new Vector3(0,Input.GetAxisRaw("Horizontal") * rotation_speed, 0));

if (Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.LeftArrow)) {
transform.Rotate(Vector3.right * Time.deltaTime);
}

Should work but i didn’t test it.

if you want to set it:

please answer my question also