How to make a gameobject have a rotation constraint?

I'm looking for how to get my player object to rotate but not past 45 degrees and -45 degrees, I sorta got this to work before but after rotating to one of the constraints, it wouldn't allow me to rotate back.

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

public class RotateTestScript : MonoBehaviour {

 // Update is called once per frame
 void Update()
 {
     if (Input.GetKey("a"))
     {
         transform.Rotate(-Vector3.forward * 15f);
     }
 }

}