Github Actions ko cosign Example

workflow.yaml

name: image

on:
  push:
    branches: ['main']
  workflow_dispatch:

permissions:
  contents: read
  packages: write
  id-token: write

jobs:
  image:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-go@v1
        with:
          go-version: 1.17.x
      - uses: sigstore/cosign-installer@v2.1.0

      # Build ko from HEAD, build and push an image tagged with the commit SHA,
      # then keylessly sign it with cosign.
      - name: Publish and sign image
        env:
          KO_DOCKER_REPO: ghcr.io/${{ github.repository }}
          COSIGN_EXPERIMENTAL: 'true'
        run: |
          go build ./
          echo "${{ github.token }}" | ./ko login ghcr.io --username "${{ github.actor }}" --password-stdin
          img=$(./ko build --bare --platform=all -t latest -t ${{ github.sha }} ./)
          echo "built ${img}"
          cosign sign ${img} \
              -a sha=${{ github.sha }} \
              -a run_id=${{ github.run_id }} \
              -a run_attempt=${{ github.run_attempt }}

Source: https://github.com/google/ko/blob/5fb6c8cf84e968bd70821fd062d0c822021e3ccf/.github/workflows/image.yaml#L25