Converting HLSL shader to work in Unreal

Development Rendering
1

Hi
Am trying to create a ‘shadow catcher’ material. I’ve found a HLSL solution but its Unity based. Can any Unreal shader gurus suggest what edits must be done?

https://forum.unity.com/threads/shadow-catcher-or-matte-shadow-shader.414418/

  Shader "Unlit/VertColorWithShadow"
  {
  Properties
  {
    _MainColor("Main Color", COLOR) = (0,0,0,1)
    _ShadowColor("Shadow Color", COLOR) = (1,0,0,1)
  }

SubShader
{
    Tags { "RenderType"="Opaque" }
    LOD 100

    Pass
    {
        Tags {"LightMode" = "ForwardBase"}

        CGPROGRAM
        #pragma multi_compile_fwdbase
        #pragma vertex vert
        #pragma fragment frag

        #include "UnityCG.cginc"
        #include "AutoLight.cginc"

        float4 _MainColor;
        float4 _ShadowColor;

        struct appdata
        {
            float4 vertex : POSITION;
        };

        struct v2f
        {
            float4 pos : SV_POSITION;
            float4 mainColor : COLOR;
            LIGHTING_COORDS(1,2)
        };
     
        v2f vert (appdata v)
        {
            v2f o;
            o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
            o.mainColor = _MainColor;

            TRANSFER_VERTEX_TO_FRAGMENT(o);

            return o;
        }
     
        fixed4 frag (v2f i) : SV_Target
        {
            fixed atten = 1.0 - LIGHT_ATTENUATION(i);
            fixed3 shadowColor = atten * _ShadowColor.rgb;
            fixed4 finalColor = i.mainColor + fixed4(shadowColor, 1.0);

            return finalColor;
        }
        ENDCG
    }

    // Pass to render object as a shadow caster
    Pass
    {
        Name "ShadowCaster"
        Tags { "LightMode" = "ShadowCaster" }
 
        ZWrite On ZTest LEqual Cull Off

        CGPROGRAM
        #pragma vertex vert
        #pragma fragment frag
        #pragma multi_compile_shadowcaster
        #include "UnityCG.cginc"

        struct v2f {
            V2F_SHADOW_CASTER;
        };

        v2f vert( appdata_base v )
        {
            v2f o;
            TRANSFER_SHADOW_CASTER_NORMALOFFSET(o)
            return o;
        }

        float4 frag( v2f i ) : SV_Target
        {
            return float4(1.0, 1.0, 1.0, 1.0);
        }
        ENDCG
    }
}
}