Fake directional light on toon shader

I'm using the basic toon shader. Probably is a silly question, I'm very new to writing shaders.

What it currently does: The UNITY_MATRIX_MV causes the model's faces to be shaded relative to the camera's view on it. This essentially gives a flashlight effect.

Desired result: A Vector material property 'Sun Direction' on the should control the direction of shading.

To illustrate, imagine a sphere. If _SunDirection = (0,-1,0), top faces should be bright and bottom dark. The intensity is controlled by the toon ramp cubemap.

Thanks in advance.

   struct appdata {
                     half4 vertex : POSITION;
                     half2 texcoord : TEXCOORD0;
                     fixed3 normal : NORMAL;
                 };
                 
                 struct v2f {
                     half4 pos : SV_POSITION;
                     half2 texcoord : TEXCOORD0;
                     half3 cubenormal : TEXCOORD1;
                     UNITY_FOG_COORDS(2)
                 };
     
                 v2f vert (appdata v)
                 {
                     v2f o;
                     o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
                     o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
                     half3 norm = v.normal;
                     o.cubenormal = mul (UNITY_MATRIX_MV, half4(v.normal,0));
                     UNITY_TRANSFER_FOG(o,o.pos);
                     return o;
                 }
     
                 fixed4 frag (v2f i) : SV_Target
                 {
                     fixed4 col = _Color * tex2D(_MainTex, i.texcoord);
                     fixed4 cube = texCUBE(_ToonShade, i.cubenormal);
                     fixed4 c = fixed4(2.0f * cube.rgb * col.rgb, col.a);
                     UNITY_APPLY_FOG(i.fogCoord, c);
                     return c;
                 }