feat(SLSA/SEC-973): container image signing action (Kong#65)

* feat(slsa/image-sign): Keyless image signing using Cosign

filter uniq registry and sign using digest

Always recursively sign manifest digests if present

* update readme for sign action

* fix readme

Signed-off-by: saisatishkarra <saisatish.karra@konghq.com>

* enable signing transaprency by default

Signed-off-by: saisatishkarra <saisatish.karra@konghq.com>

---------

Signed-off-by: saisatishkarra <saisatish.karra@konghq.com>

.github/workflows/docker-image-sign.yml

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+name: Docker Sign Test
+
+on:
+  pull_request:
+    branches:
+    - main
+  push:
+    branches:
+    - main
+    tags:
+    - '*'
+  workflow_dispatch: {}
+
+jobs:
+  test-sign-docker-image:
+
+    permissions:
+      contents: read
+      packages: write # needed to upload to packages to registry
+      id-token: write # needed for signing the images with GitHub OIDC Token
+
+    if: ${{ github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository }}
+    name: Test Sign Docker Image
+    runs-on: ubuntu-22.04
+    env:
+      PRERELEASE_IMAGE: kongcloud/security-test-repo-pub:ubuntu_23_10 #particular reason for the choice of image: test multi arch image
+      TAGS: kongcloud/security-test-repo-pub:ubuntu_23_10,kongcloud/security-test-repo:ubuntu_23_10
+    steps:
+
+    - uses: actions/checkout@v3
+
+    - name: Install regctl
+      uses: regclient/actions/regctl-installer@main
+
+    - name: Parse Image Manifest Digest
+      id: image_manifest_metadata
+      run: |
+        manifest_list_exists="$(
+          if regctl manifest get "${PRERELEASE_IMAGE}" --format raw-body --require-list -v panic &> /dev/null; then
+            echo true
+          else
+            echo false
+          fi
+        )"
+        echo "manifest_list_exists=$manifest_list_exists"
+        echo "manifest_list_exists=$manifest_list_exists" >> $GITHUB_OUTPUT
+
+        manifest_sha="$(regctl image digest "${PRERELEASE_IMAGE}")"
+
+        echo "manifest_sha=$manifest_sha"
+        echo "manifest_sha=$manifest_sha" >> $GITHUB_OUTPUT
+
+    - name: Sign Image digest
+      id: sign_image
+      if: steps.image_manifest_metadata.outputs.manifest_sha != ''
+      uses: ./security-actions/sign-docker-image
+      with:
+        cosign_output_prefix: ubuntu-23-10
+        signature_registry: kongcloud/security-test-repo-sig-pub
+        tags: ${{ env.TAGS }} 
+        image_digest: ${{ steps.image_manifest_metadata.outputs.manifest_sha }}
+        local_save_cosign_assets: true
+        registry_username: ${{ secrets.DOCKERHUB_PUSH_USERNAME }}
+        registry_password: ${{ secrets.DOCKERHUB_PUSH_TOKEN }}
+
+    - name: Push Images
+      env:
+        RELEASE_TAG: kongcloud/security-test-repo:v1
+      run: |
+        docker pull ${PRERELEASE_IMAGE}
+        for tag in $RELEASE_TAG; do
+          regctl -v debug image copy ${PRERELEASE_IMAGE} $tag
+        done
+    
+    - name: Sign Image digest
+      id: sign_image_v1
+      if: steps.image_manifest_metadata.outputs.manifest_sha != ''
+      uses: ./security-actions/sign-docker-image
+      env:
+        RELEASE_TAG: kongcloud/security-test-repo:v1
+      with:
+        cosign_output_prefix: v1 # Optional
+        local_save_cosign_assets: true # Optional
+        signature_registry: kongcloud/security-test-repo-sig-pub
+        tags: ${{ env.RELEASE_TAG }} 
+        image_digest: ${{ steps.image_manifest_metadata.outputs.manifest_sha }}
+        registry_username: ${{ secrets.DOCKERHUB_PUSH_USERNAME }}
+        registry_password: ${{ secrets.DOCKERHUB_PUSH_TOKEN }}

security-actions/sign-docker-image/README.md

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+# Security actions
+
+## Action implemented
+
+- [Sign Docker Image](./sign-docker-image/action.yml) is a unified action for container image signing. The action leverages keyless signing to produce an Signature and uploads to Docker Image layer and Public Rekor for transaprency.
+
+- Tools used:
+    - [Cosign](https://github.com/sigstore/cosign)
+### Signing Docker Image
+
+- For workflows where image artifact are being pushed to the registry, this needs to be implemented `after the scan and before the publish` step.
+
+#### Workflow / Job Permissions for Keyless OIDC Signing:
+```yaml
+permissions:
+  packages: write
+  id-token: write # needed for signing the images with GitHub OIDC Token
+```
+
+#### Signature Publishing
+- `cosign sign` to:
+  -  Generate an signature based on keyless identities using `Github` OIDC provider within workflows
+- Be authenicated access to publish docker hub registry
+- Uploads the [mapping identities](https://github.com/sigstore/fulcio/blob/main/docs/oid-info.md) to Public Rekor Instance logged forever.
+  - **May Contain senstitive information for private repositories**; Yet no way to protect PII being uploaded / masked.
+
+#### Verification
+- `cosign verify` needs to have:
+  - access to public rekor instance
+  - authenicated access to private docker hub registry
+  - un-authenticated access to public registry
+
+#### Input specification
+
+#### Parameters
+```yaml
+  local_save_cosign_assets:
+    description: 'Save cosign output assets locally on disk. Ex: certificate and signature of signed artifacts'
+    required: false
+    default: false
+  cosign-output-prefix:
+    description: 'cosign output prefix. Ex: certificate and signature of signed artifacts'
+    required: true
+  signature_registry:
+    description: 'Separate registry to store image signature to avoid polluting image registry'
+    required: false
+    default: ''
+  tags:
+    description: 'Comma separated <image>:<tag> that have same digest'
+    required: true
+  image_digest:
+    description: 'specify single sha256 digest associated with the specified image_registries'
+    required: true
+  registry_username:
+    description: 'docker username to login against private docker registry'
+    required: false
+  registry_password:
+    description: 'docker password to login against private docker registry'
+    required: false
+
+```
+#### Output specification
+
+- Generates a signature that is pushed to registry for every single platform and manifest digest
+
+- Generates a log entry in Public Rekor transaprency for every digest being signed with a unique docker repository
+
+- No Build Time artifacts are generated
+
+#### Verification:
+Use `cosign verify` command to specify claims and image digest to be verified against the rekor transaparency log and signature / certificate subject identity in the Docker registry
+
+Example:
+```
+COSIGN_REPOSITORY=kong/notary cosign verify -a repo="Kong/kong-ee" -a workflow="Package & Release" --certificate-oidc-issuer="https://token.actions.githubusercontent.com" --certificate-identity-regexp="https://github.com/Kong/kong-ee/.github/workflows/release.yml*" <image>:<tag>@sha256:<disgest> 
+```
+
+#### Usage Examples
+
+  ```yaml
+  jobs:
+  test-sign-docker-image:
+
+    permissions:
+      contents: read
+      packages: write # needed to upload to packages to registry
+      id-token: write # needed for signing the images with GitHub OIDC Token
+
+    if: ${{ github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository }}
+    name: Test Sign Docker Image
+    runs-on: ubuntu-22.04
+    env:
+      PRERELEASE_IMAGE: kongcloud/security-test-repo-pub:ubuntu_23_10 #particular reason for the choice of image: test multi arch image
+      TAGS: kongcloud/security-test-repo-pub:ubuntu_23_10,kongcloud/security-test-repo:ubuntu_23_10
+    steps:
+
+    - uses: actions/checkout@v3
+
+    - name: Install regctl
+      uses: regclient/actions/regctl-installer@main
+
+    - name: Parse Image Manifest Digest
+      id: image_manifest_metadata
+      run: |
+        manifest_list_exists="$(
+          if regctl manifest get "${PRERELEASE_IMAGE}" --format raw-body --require-list -v panic &> /dev/null; then
+            echo true
+          else
+            echo false
+          fi
+        )"
+        echo "manifest_list_exists=$manifest_list_exists"
+        echo "manifest_list_exists=$manifest_list_exists" >> $GITHUB_OUTPUT
+
+        manifest_sha="$(regctl image digest "${PRERELEASE_IMAGE}")"
+
+        echo "manifest_sha=$manifest_sha"
+        echo "manifest_sha=$manifest_sha" >> $GITHUB_OUTPUT
+
+    - name: Sign Image digest
+      id: sign_image_pre_release
+      if: steps.image_manifest_metadata.outputs.manifest_sha != ''
+      uses: ./security-actions/sign-docker-image
+      with:
+        cosign_output_prefix: ubuntu-23-10
+        signature_registry: kongcloud/security-test-repo-sig-pub
+        tags: ${{ env.TAGS }} 
+        image_digest: ${{ steps.image_manifest_metadata.outputs.manifest_sha }}
+        local_save_cosign_assets: true
+        registry_username: ${{ secrets.GHA_DOCKERHUB_PUSH_USER }}
+        registry_password: ${{ secrets.GHA_KONG_ORG_DOCKERHUB_PUSH_TOKEN }}
+
+    - name: Push Images
+      env:
+        RELEASE_TAG: kongcloud/security-test-repo:v1
+      run: |
+        docker pull ${PRERELEASE_IMAGE}
+        for tag in $RELEASE_TAG; do
+          regctl -v debug image copy ${PRERELEASE_IMAGE} $tag
+        done
+    
+    - name: Sign Image digest
+      id: sign_image_promotion
+      if: steps.image_manifest_metadata.outputs.manifest_sha != ''
+      uses: ./security-actions/sign-docker-image
+      env:
+        RELEASE_TAG: kongcloud/security-test-repo:v1
+      with:
+        cosign_output_prefix: v1
+        signature_registry: kongcloud/security-test-repo-sig-pub
+        tags: ${{ env.RELEASE_TAG }} 
+        image_digest: ${{ steps.image_manifest_metadata.outputs.manifest_sha }}
+        local_save_cosign_assets: true
+        registry_username: ${{ secrets.GHA_DOCKERHUB_PUSH_USER }}
+        registry_password: ${{ secrets.GHA_DOCKERHUB_PUSH_TOKEN }}
+  ```

security-actions/sign-docker-image/action.yml

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+name: Sign Docker Image
+description: Keyeless Image signing with transaprency and uploads to registry for specified docker image
+author: 'Kong'
+inputs:
+  local_save_cosign_assets:
+    description: 'Save cosign output assets locally on disk. Ex: certificate and signature of signed artifacts'
+    required: false
+    default: false
+  cosign_output_prefix:
+    description: 'cosign file prefix for storing local signatures and certificates. Works when input local_save_cosign_assets is enabled'
+    required: false
+    default: ''
+  signature_registry:
+    description: 'Separate registry to store image signature to avoid polluting image registry'
+    required: false
+    default: ''
+  tags:
+    description: 'Comma separated <image>:<tag> that have same digest'
+    required: true
+  image_digest:
+    description: 'specify single sha256 digest associated with the specified image_registries'
+    required: true
+  registry_username:
+    description: 'docker username to login against private docker registry'
+    required: false
+  registry_password:
+    description: 'docker password to login against private docker registry'
+    required: false
+
+#outputs:
+  # sbom-cyclonedx-report:
+  #   description: 'SBOM cyclonedx report'
+  #   value: ${{ steps.meta.outputs.sbom_cyclonedx_file }}
+
+runs:
+  using: composite
+  steps:
+
+    - name: Set Cosign metadata
+      shell: bash
+      id: meta
+      env:
+        LOCAL_SAVE_COSIGN_ASSETS: ${{ inputs.local_save_cosign_assets }}
+        ASSET_PREFIX: ${{ inputs.cosign_output_prefix }}
+      run: $GITHUB_ACTION_PATH/scripts/cosign-metadata.sh
+
+    - name: Install Cosign
+      uses: sigstore/cosign-installer@v3.1.1
+
+    - name: Check install!
+      shell: bash
+      run: cosign version
+
+    - name: Setup image namespace for signing, strip off the tag
+      shell: bash
+      env: 
+        INPUT_TAGS: ${{ inputs.tags }}
+      run: |
+        set -euox pipefail
+
+        TAGS="${INPUT_TAGS//,/ }"
+
+        IMAGE_REPOS=$(for tag in \
+          `echo "${TAGS}"`; do
+          echo -n "${tag}" | awk -F ":" '{print $1}' -;done|sort -u)
+        
+          echo $IMAGE_REPOS
+
+          echo 'IMAGES<<EOF' >> $GITHUB_ENV
+          echo $IMAGE_REPOS >> $GITHUB_ENV
+          echo 'EOF' >> $GITHUB_ENV
+
+    - name: Login to Container Registry
+      uses: docker/login-action@v2.1.0
+      if: ${{ inputs.registry_username != '' && inputs.registry_password != '' }}
+      with:
+        username: ${{ inputs.registry_username }}
+        password: ${{ inputs.registry_password }}
+
+    - name: Sign the images with GitHub OIDC Token 
+      id: sign
+      env:
+        COSIGN_REPOSITORY: ${{ inputs.signature_registry }}
+        COSIGN_ARGS: ${{ steps.meta.outputs.cosign_signing_args}}
+        IMAGE_REGISTRIES: ${{ env.IMAGES }} # Space separated image registries that have same digest
+        IMAGE_DIGEST: ${{ inputs.image_digest }} # Single Digest associated with the registry images 
+      shell: bash
+      run: |
+        set -euox pipefail
+        for img in $IMAGES; do
+          cosign sign ${{ env.COSIGN_ARGS }} \
+          -a "repo=${{ github.repository }}" \
+          -a "workflow=${{ github.workflow }}" \
+          -a "sha=${{ github.sha }}" \
+          "$img"@${{ env.IMAGE_DIGEST }}
+        done
+
+     # Upload Cosign Artifacts (public cert and signatures)
+    - name: Upload Cosign Artifacts
+      uses: actions/upload-artifact@v3
+      if: ${{ inputs.local_save_cosign_assets == 'true' && inputs.cosign_output_prefix != '' }}
+      with:
+        name: signed-image-assets
+        path: |
+          ${{inputs.cosign_output_prefix}}*.crt
+          ${{inputs.cosign_output_prefix}}.sig*
+        if-no-files-found: warn

security-actions/sign-docker-image/scripts/cosign-metadata.sh

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+#!/usr/bin/env bash
+
+set -euo pipefail
+
+readonly signature_ext=".sig"
+readonly signing_cert_ext=".crt"
+
+readonly rekor_transparency="true"
+
+# Always Recurisvely sign one/ all manifest digests for docker manifest distribution /list mediaType
+signing_args="--yes --recursive --tlog-upload=${rekor_transparency}"
+
+# if [[ ${MULTI_PLATFORM} ]]; then
+#     signing_args+=" --recursive"
+# fi
+
+if [[ "${LOCAL_SAVE_COSIGN_ASSETS}" == "true" ]]; then
+    if [[ -n "${ASSET_PREFIX}" ]]; then
+        signature_file="${ASSET_PREFIX##*/}${signature_ext}"
+        certificate_file="${ASSET_PREFIX##*/}${signing_cert_ext}"
+    else
+        echo '::error ::set input cosign_output_prefix in $0'
+        exit 1
+    #     signature_file="${ASSET_PREFIX##*/}${signature_ext}"
+    #     certificate_file="${ASSET_PREFIX##*/}${signing_cert_ext}"
+    fi
+
+    echo "signature_file=${signature_file}" >> $GITHUB_OUTPUT
+    echo "certificate_file=${certificate_file}" >> $GITHUB_OUTPUT
+    signing_args+=" --output-certificate=${certificate_file} --output-signature=${signature_file}"
+fi
+
+echo "COSIGN SIGNING ARGS: ${signing_args}"
+echo "cosign_signing_args=${signing_args}" >> $GITHUB_OUTPUT