`actions/attest`

Generate signed attestations for workflow artifacts. Internally powered by the @actions/attest package.

Attestations bind some subject (a named artifact along with its digest) to a predicate (some assertion about that subject) using the in-toto format. Predicates consist of a type URI and a JSON object containing type-dependent parameters.

A verifiable signature is generated for the attestation using a short-lived Sigstore-issued signing certificate. If the repository initiating the GitHub Actions workflow is public, the public-good instance of Sigstore will be used to generate the attestation signature. If the repository is private/internal, it will use the GitHub private Sigstore instance.

Once the attestation has been created and signed, it will be uploaded to the GH attestations API and associated with the repository from which the workflow was initiated.

Attestations can be verified using the attestation command in the GitHub CLI.

See Using artifact attestations to establish provenance for builds for more information on artifact attestations.

Note

Artifact attestations are available in public repositories for all current GitHub plans.

To use artifact attestations in private or internal repositories, you must be on a GitHub Enterprise Cloud plan.

Artifact attestations are NOT supported on GitHub Enterprise Server.

Usage

Within the GitHub Actions workflow which builds some artifact you would like to attest:

Ensure that the following permissions are set:
```
permissions:
  id-token: write
  attestations: write
```
The id-token permission gives the action the ability to mint the OIDC token necessary to request a Sigstore signing certificate. The attestations permission is necessary to persist the attestation.
Add the following to your workflow after your artifact has been built:
```
- uses: actions/attest@v2
  with:
    subject-path: '<PATH TO ARTIFACT>'
    predicate-type: '<PREDICATE URI>'
    predicate-path: '<PATH TO PREDICATE>'
```
The subject-path parameter should identify the artifact for which you want to generate an attestation. The predicate-type can be any of the the vetted predicate types or a custom value. The predicate-path identifies a file containing the JSON-encoded predicate parameters.

Inputs

See action.yml

- uses: actions/attest@v2
  with:
    # Path to the artifact serving as the subject of the attestation. Must
    # specify exactly one of "subject-path", "subject-digest", or
    # "subject-checksums". May contain a glob pattern or list of paths
    # (total subject count cannot exceed 1024).
    subject-path:

    # SHA256 digest of the subject for the attestation. Must be in the form
    # "sha256:hex_digest" (e.g. "sha256:abc123..."). Must specify exactly one
    # of "subject-path", "subject-digest", or "subject-checksums".
    subject-digest:

    # Subject name as it should appear in the attestation. Required when
    # identifying the subject with the "subject-digest" input.
    subject-name:

    # Path to checksums file containing digest and name of subjects for
    # attestation. Must specify exactly one of "subject-path", "subject-digest",
    # or "subject-checksums".
    subject-checksums:

    # URI identifying the type of the predicate.
    predicate-type:

    # String containing the value for the attestation predicate. String length
    # cannot exceed 16MB. Must supply exactly one of "predicate-path" or
    # "predicate".
    predicate:

    # Path to the file which contains the content for the attestation predicate.
    # File size cannot exceed 16MB. Must supply exactly one of "predicate-path"
    # or "predicate".
    predicate-path:

    # Whether to push the attestation to the image registry. Requires that the
    # "subject-name" parameter specify the fully-qualified image name and that
    # the "subject-digest" parameter be specified. Defaults to false.
    push-to-registry:

    # Whether to attach a list of generated attestations to the workflow run
    # summary page. Defaults to true.
    show-summary:

    # The GitHub token used to make authenticated API requests. Default is
    # ${{ github.token }}
    github-token:

Outputs

Name	Description	Example
`attestation-id`	GitHub ID for the attestation	`123456`
`attestation-url`	URL for the attestation summary	`https://github.com/foo/bar/attestations/123456`
`bundle-path`	Absolute path to the file containing the generated attestation	`/tmp/attestation.json`

Attestations are saved in the JSON-serialized Sigstore bundle format.

If multiple subjects are being attested at the same time, a single attestation will be created with references to each of the supplied subjects.

Attestation Limits

Subject Limits

No more than 1024 subjects can be attested at the same time.

Predicate Limits

Whether supplied via the predicate or predicatePath input, the predicate string cannot exceed 16MB.

Examples

Identify Subject by Path

For the basic use case, simply add the attest action to your workflow and supply the path to the artifact for which you want to generate attestation.

name: build-attest

on:
  workflow_dispatch:

jobs:
  build:
    permissions:
      id-token: write
      contents: read
      attestations: write

    steps:
      - name: Checkout
        uses: actions/checkout@v4
      - name: Build artifact
        run: make my-app
      - name: Attest
        uses: actions/attest@v2
        with:
          subject-path: '${{ github.workspace }}/my-app'
          predicate-type: 'https://example.com/predicate/v1'
          predicate: '{}'

Identify Multiple Subjects

If you are generating multiple artifacts, you can attest all of them at the same time by using a wildcard in the subject-path input.

- uses: actions/attest@v2
  with:
    subject-path: 'dist/**/my-bin-*'
    predicate-type: 'https://example.com/predicate/v1'
    predicate: '{}'

For supported wildcards along with behavior and documentation, see @actions/glob which is used internally to search for files.

Alternatively, you can explicitly list multiple subjects with either a comma or newline delimited list:

- uses: actions/attest@v2
  with:
    subject-path: 'dist/foo, dist/bar'

- uses: actions/attest@v2
  with:
    subject-path: |
      dist/foo
      dist/bar

Identify Subjects with Checksums File

If you are using tools like goreleaser or jreleaser which generate a checksums file you can identify the attestation subjects by passing the path of the checksums file to the subject-checksums input. Each of the artifacts identified in the checksums file will be listed as a subject for the attestation.

- name: Calculate artifact digests
  run: |
    shasum -a 256 foo_0.0.1_* > subject.checksums.txt

- uses: actions/attest@v2
  with:
    subject-checksums: subject.checksums.txt
    predicate-type: 'https://example.com/predicate/v1'
    predicate: '{}'

The file referenced by the subject-checksums input must conform to the same format used by the shasum tools. Each subject should be listed on a separate line including the hex-encoded digest (either SHA256 or SHA512), a space, a single character flag indicating either binary (*) or text ( ) input mode, and the filename.

b569bf992b287f55d78bf8ee476497e9b7e9d2bf1c338860bfb905016218c740  foo_0.0.1_darwin_amd64
a54fc515e616cac7fcf11a49d5c5ec9ec315948a5935c1e11dd610b834b14dde  foo_0.0.1_darwin_arm64

Container Image

When working with container images you can invoke the action with the subject-name and subject-digest inputs.

If you want to publish the attestation to the container registry with the push-to-registry option, it is important that the subject-name specify the fully-qualified image name (e.g. "ghcr.io/user/app" or "acme.azurecr.io/user/app"). Do NOT include a tag as part of the image name -- the specific image being attested is identified by the supplied digest.

NOTE: When pushing to Docker Hub, please use "docker.io" as the registry portion of the image name.

name: build-attested-image

on:
  push:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    permissions:
      id-token: write
      packages: write
      contents: read
      attestations: write
    env:
      REGISTRY: ghcr.io
      IMAGE_NAME: ${{ github.repository }}

    steps:
      - name: Checkout
        uses: actions/checkout@v4
      - name: Login to GitHub Container Registry
        uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}
      - name: Build and push image
        id: push
        uses: docker/build-push-action@v5.0.0
        with:
          context: .
          push: true
          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest
      - name: Attest
        uses: actions/attest@v2
        id: attest
        with:
          subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          subject-digest: ${{ steps.push.outputs.digest }}
          predicate-type: 'https://in-toto.io/attestation/release/v0.1'
          predicate: '{"purl":"pkg:oci/..."}'
          push-to-registry: true

License

aqsa326/attest

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