Make my volumetric cloud code cast shadows

Hi, I have a cloud rendering shader that uses 3d noise and raymarching. It's a screen-wide frag shader, base on this tutorial: https://www.youtube.com/watch?v=4QOcCGI6xOU

Currently, I illuminate the clouds using yet more raymarching. I have two problems with that, first it's expensive, second my clouds don't cast any shadows.

I want to basically tell Unity to write to the dynamic lightmap, and use it to abort the lightmarching if I know I'm the shadow of the cloud.

I have little idea on how to do that, except vaguely that adding a shadow pass to the shader will tell unity to do that.

Here's my current code structure, minus the very long raymarching code:

 Shader "Jupiter/Clouds"
 {
 
     Properties
     {
         _MainTex ("Texture", 2D) = "white" {}
     }
     SubShader
     {
     
         // No culling or depth
         Cull Off ZWrite Off ZTest Always
 
         Pass
         {
             CGPROGRAM
 
             #pragma vertex vert
             #pragma fragment frag
 
             #include "UnityCG.cginc"
             #include "Assets/Scripts/Clouds/Shaders/CloudDebug.cginc"
 
             // vertex input: position, UV
             struct appdata {
                 float4 vertex : POSITION;
                 float2 uv : TEXCOORD0;
             };
 
             struct v2f {
                 float4 pos : SV_POSITION;
                 float2 uv : TEXCOORD0;
                 float3 viewVector : TEXCOORD1;
             };
   
             v2f vert (appdata v) {
                 v2f output;
                 output.pos = UnityObjectToClipPos(v.vertex);
                 output.uv = v.uv;
                 // Camera space matches OpenGL convention where cam forward is -z. In unity forward is positive z.
                 // (https://docs.unity3d.com/ScriptReference/Camera-cameraToWorldMatrix.html)
                 float3 viewVector = mul(unity_CameraInvProjection, float4(v.uv * 2 - 1, 0, -1));
                 output.viewVector = mul(unity_CameraToWorld, float4(viewVector,0));
                 return output;
             }
 
             // Textures
             Texture3D<float4> NoiseTex;
             Texture3D<float4> DetailNoiseTex;
             Texture2D<float4> WeatherMap;
             Texture2D<float4> BlueNoise;
   
             SamplerState samplerNoiseTex;
             SamplerState samplerDetailNoiseTex;
             SamplerState samplerWeatherMap;
             SamplerState samplerBlueNoise;
 
             sampler2D _MainTex;
             sampler2D _CameraDepthTexture;
 
             //tons of parameters
 
             float4 frag (v2f i) : SV_Target
             {
                 //blablabla
                 return float4(col,0);
 
             }
 
             ENDCG
         }
     }
 }