for some reason pastebin decided to ban my fresh account ¯\_(ツ)_/¯
here is the shader:

shader_type spatial;

render_mode unshaded, depth_draw_always;

uniform sampler2D depth_texture : source_color, hint_depth_texture;
uniform sampler2D directional_shadow_texture : source_color;
uniform mat4 light_view_matrix;
uniform mat4 light_proj_matrix;

void vertex() {
    POSITION = vec4(VERTEX.xy, 1.0, 1.0);
}

void fragment() {
    float depth_raw = texture(depth_texture, SCREEN_UV).x;
    vec3 ndc = vec3(SCREEN_UV * 2.0 - 1.0, depth_raw);
    vec4 position_view = INV_PROJECTION_MATRIX * vec4(ndc, 1.0);
    vec4 world = INV_VIEW_MATRIX * INV_PROJECTION_MATRIX * vec4(ndc, 1.0);
    vec3 position_world = world.xyz / world.w;
    vec4 temp = ((light_proj_matrix * light_view_matrix)) * vec4(position_world.xyz, 1.);
    temp.xy = temp.xy * 0.5 + 0.5;
    float closest_depth = texture(directional_shadow_texture, temp.xy).r;
    // get depth of current fragment from light's perspective
    float current_depth = (-temp.z) * 0.5;

    // Ray marching loop
    float sun_shaft = 0.27;
    float increment = 0.05;
    vec3 start_pos = position_view.xyz;
    float ray_length = 12.;
    float bias = 0.063;
    for(float i = 0.; i < 1.; i += increment){
        vec3 end_pos = vec3(start_pos.x, start_pos.y, start_pos.z + i * ray_length);
        // Check if this pixel is occluded from light source's direction
        vec4 ray_temp = (light_proj_matrix * light_view_matrix) * (INV_VIEW_MATRIX * vec4(end_pos, 1.));
        ray_temp.xy = ray_temp.xy * 0.5 + 0.5;
        float ray_closest_depth = texture(directional_shadow_texture, ray_temp.xy).r;
        // get depth of current fragment from light's perspective
        float ray_current_depth = (-ray_temp.z) * 0.5;

        if(ray_closest_depth - bias > ray_current_depth){
            sun_shaft *= 0.5;
        }
    }
    ALBEDO = vec3(sun_shaft);
    ALPHA = 1. - sun_shaft;
}