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https://github.com/actions/attest

Action for generating attestations for workflow artifacts
https://github.com/actions/attest

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Action for generating attestations for workflow artifacts

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# `actions/attest`



Generate signed attestations for workflow artifacts. Internally powered by the

[@actions/attest][1] package.



Attestations bind some subject (a named artifact along with its digest) to a

predicate (some assertion about that subject) using the [in-toto][2] format.

[Predicates][3] 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][4]-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][5].



See [Using artifact attestations to establish provenance for builds][9] 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:



1. Ensure that the following permissions are set:



   ```yaml

   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.



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



   ```yaml

   - uses: actions/attest@v2

     with:

       subject-path: ''

       predicate-type: ''

       predicate-path: ''

   ```



   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][3] or a custom value. The `predicate-path`

   identifies a file containg the JSON-encoded predicate parameters.



### Inputs



See [action.yml](action.yml)



```yaml

- 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][6] 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.



```yaml

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.



```yaml

- 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][8] which is used internally to search for files.



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

newline delimited list:



```yaml

- uses: actions/attest@v2

  with:

    subject-path: 'dist/foo, dist/bar'

```



```yaml

- uses: actions/attest@v2

  with:

    subject-path: |

      dist/foo

      dist/bar

```



### Identify Subjects with Checksums File



If you are using tools like

[goreleaser](https://goreleaser.com/customization/checksum/) or

[jreleaser](https://jreleaser.org/guide/latest/reference/checksum.html) 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.



```yaml

- 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.



```text

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.



```yaml

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/[email protected]

        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

```



[1]: https://github.com/actions/toolkit/tree/main/packages/attest

[2]: https://github.com/in-toto/attestation/tree/main/spec/v1

[3]:

  https://github.com/in-toto/attestation/tree/main/spec/predicates#in-toto-attestation-predicates

[4]: https://www.sigstore.dev/

[5]: https://cli.github.com/manual/gh_attestation_verify

[6]:

  https://github.com/sigstore/protobuf-specs/blob/main/protos/sigstore_bundle.proto

[8]: https://github.com/actions/toolkit/tree/main/packages/glob#patterns

[9]:

  https://docs.github.com/en/actions/security-guides/using-artifact-attestations-to-establish-provenance-for-builds