A basic example of a ThreeJS (r108) ShaderMaterial with shadows, fog and dithering support.

BasicCustomShader.js

import { mergeUniforms } from 'three/src/renderers/shaders/UniformsUtils.js'
import { UniformsLib } from 'three/src/renderers/shaders/UniformsLib.js'

export default {

  uniforms: mergeUniforms([
    UniformsLib.lights,
    UniformsLib.fog,
  ]),

  vertexShader: `
    #include <common>
    #include <fog_pars_vertex>
    #include <shadowmap_pars_vertex>

    void main() {
      #include <begin_vertex>
      #include <project_vertex>
      #include <worldpos_vertex>
      #include <shadowmap_vertex>
      #include <fog_vertex>
    }
  `,

  fragmentShader: `
    #include <common>
    #include <packing>
    #include <fog_pars_fragment>
    #include <bsdfs>
    #include <lights_pars_begin>
    #include <shadowmap_pars_fragment>
    #include <shadowmask_pars_fragment>
    #include <dithering_pars_fragment>

    void main() {
      // CHANGE THAT TO YOUR NEEDS
      // ------------------------------
      vec3 finalColor = vec3(0, 0.75, 0);
      vec3 shadowColor = vec3(0, 0, 0);
      float shadowPower = 0.5;
      // ------------------------------
      
      // it just mixes the shadow color with the frag color
      gl_FragColor = vec4( mix(finalColor, shadowColor, (1.0 - getShadowMask() ) * shadowPower), 1.0);

      #include <fog_fragment>
      #include <dithering_fragment>
    }
  `
};

my-project.js

import BasicCustomShader from 'BasicCustomShader.js'

// and here is how to create the material
const material = new THREE.ShaderMaterial({
  ...BasicCustomShader,
  fog: true,
  lights: true,
  dithering: true,
});

// PS : you should also set `receiveShadow = true` on your mesh !

add this includes to the vertex shader

#include <begin_vertex>

#include <beginnormal_vertex>     // Defines objectNormal

#include <project_vertex>

#include <worldpos_vertex>

#include <defaultnormal_vertex>   // Defines transformedNormal

#include <shadowmap_vertex>