Specular map to decide reflection

Hi!

Im a programmer who got the task to create a shader. This shader should act like the builtin Transparent/Cutout/Bumped specular but with one difference. It should take a specular map and use that as Alpha/Transparency/Whatever it's called (that decide how much he light should reflect)

I can't for the love of my life seem to find anything anywhere. The closest i've got is the source code for the (original builtin) shader itself:

 Shader "Transparent/Cutout/Bumped Specular"
 {
         Properties
         {
             _Color ("Main Color", Color) = (1,1,1,1)
             _SpecColor ("Specular Color", Color) = (0.5, 0.5, 0.5, 0)
             _Shininess ("Shininess", Range (0.01, 1)) = 0.078125
             _MainTex ("Base (RGB) TransGloss (A)", 2D) = "white" {}
             _BumpMap ("Normalmap", 2D) = "bump" {}
             _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
         }
  
         SubShader
         {
             Tags {"Queue"="AlphaTest" "IgnoreProjector"="True" "RenderType"="TransparentCutout"}
             LOD 400
  
                 CGPROGRAM
                 #pragma surface surf BlinnPhong alphatest:_Cutoff
  
                 sampler2D _MainTex;
                 sampler2D _BumpMap;
                 fixed4 _Color;
                 half _Shininess;
  
                 struct Input
                 {
                     float2 uv_MainTex;
                     float2 uv_BumpMap;
                 };
  
                 void surf (Input IN, inout SurfaceOutput o)
                 {
                     fixed4 tex = tex2D(_MainTex, IN.uv_MainTex);
                     o.Albedo = tex.rgb * _Color.rgb;
                     o.Gloss = tex.a;
                     o.Alpha = tex.a * _Color.a;
                     o.Specular = _Shininess;
                     o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
                 }
                 ENDCG
         }
         FallBack "Transparent/Cutout/VertexLit"
 }