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.

Usage

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

1. 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.

2. Add the following to your workflow after your artifact has been built:

   - uses: actions/attest@v1
     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 containg the JSON-encoded predicate parameters.

Inputs

See action.yml

- uses: actions/attest@v1
  with:
    # Path to the artifact serving as the subject of the attestation. Must
    # specify exactly one of "subject-path" or "subject-digest". May contain
    # a glob pattern or list of paths (total subject count cannot exceed 2500).
    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" or "subject-digest".
    subject-digest:

    # Subject name as it should appear in the attestation. Required unless
    # "subject-path" is specified, in which case it will be inferred from the
    # path.
    subject-name:

    # 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
bundle-path	Absolute path to the file containing the generated attestation	/tmp/attestation.jsonl

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

If multiple subjects are being attested at the same time, each attestation will be written to the output file on a separate line (using the JSON Lines format).

Attestation Limits

Subject Limits

No more than 2500 subjects can be attested at the same time. Subjects will be processed in batches 50. After the initial group of 50, each subsequent batch will incur an exponentially increasing amount of delay (capped at 1 minute of delay per batch) to avoid overwhelming the attestation API.

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@v1
        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 generate an attestation for each by using a wildcard in the subject-path input.

- uses: actions/attest@v1
  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@v1
  with:
    subject-path: 'dist/foo, dist/bar'

- uses: actions/attest@v1
  with:
    subject-path: |
      dist/foo
      dist/bar

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@v1
        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